Visual Mode: changes to Eternity Engine's upper/lower texture skewing definitions are now shown in Visual Mode

Visual Mode: fixed a crash when toggling visual vertex slope picking and the map contains double-sided linedefs without a front sidedef. Fixes #928

- fixed a rare condition where skewed mid textures were not clipped correctly
- fixed a problem where translucent mid textures were not skewed correctly
- fixed a problem where sprites were skewed unintentionally

Draw Grid Mode: fixed a problem where "continuous drawing" would redraw all previously drawn shapes each time a drawing was finished. Fixes #912

Added action to change the index of linedefs, things, sectors, and vertices. Can be accessed through a shortcut (not bound by default) or the menu of the respective mode (#903)

Edit Selection Mode: fixed a problem where floor and ceiling textures were unintentionally scaled in UDMF when resizing the selection. Fixes #873

Map Analysis Mode: fixed a problem where lines with fractional vertex positions could erroneously be reported as overlapping

Disabled visual sloping for game configurations that do not support plane equation slopes. Fixes #828
Added toasts for visual sloping events

Behavior can be configured in the "Toasts" tab in the preferences.

Tag Range plugin: fixed a problem where the new tags were not displayed in Sectors Mode when selection numbering was disabled. Fixes #795

Sectors Mode: fixed a regression where sector labels were not updated after editing sectors. Fixes #793

Fixed a regression where editing map elements did not preserve the selection order, but used the index order instead. Fixes #791

- editing a highlighted, not selected map element will deselect other selected map elements, then start editing the highlighted map element
- dragging a highlighted, not selected map element will deselect other selected map elements, then start dragging the highlighted map element
- dragging a single map element will keep its selection state. I.e. dragging a selected map element will not deselect it after dragging anymore
  - dragging a highlighted, not selected thing will not select it after dragging
- dragging a highlighted, not selected sector, while other sectors are selected, will only drag the highlighted sector, and not the selected sector (and deselect the selected sectors)

Linedefs Mode: fixed a problem where the "Select Single-sided only" and "Select Double-sided only" actions would still display the selection numbers of deselected linedefs

Visual Mode: fixed an issue where using the "apply camera rotation to things" action did not update the thing cages properly

Draw Settings docker: fixed an issue where toggling the texture check boxes stopped texture overrides from being applied

Map element associations: fixed a problem where things that have a argument of type tag set to 0 were referencing all things with tag 0. Fixes #718

Linedefs Mode: fixed a crash that could happen when the mouse was moved out of the map control while an UDBScript was modifying the map

Sectors Mode: fixed a crash that could happen when the mouse was moved out of the map control while an UDBScript was modifying the map

Edit Selection Mode: improved handling of texture transformation (still doesn't work 100% correctly)

Map Analysis Mode: fixed an issue where lines were erroneously reported as overlapping in certain situations. Fixes #713

Visual Mode: Fixed a problem where using visual sloping a slope handle around itself resulted in invalid slopes

Copy and Paste Properties: fixed a problem where the "fadecolor" GZDoom UDMF sector property was not copied/pasted

Visual Mode: fixed a problem where offsetting the middle texture of double sided lines would not work under certain circumstances. Fixes #702

* Extended rendering options for drawing vertices
* Fixed vertex scale slider behaviour
* Force plot highlighted vertex in DragSectorsMode
* Moved ShouldRenderVertices property into the properties region
* made config file variable lower case to be in line with other config file variables

Visual Mode: added actions to lower and raise map elements by the current grid size (no defaults bound). Resolves #699

Snap selection to grid: fixed a problem that could cause a crash if geometry got removed by snapping it to the grid