Thing-based vertex slopes: Pick the right mapthings

See merge request STJr/UltimateZoneBuilder!3

Merge current state of UDB

See merge request STJr/UltimateZoneBuilder!2

The calls to native windows functions wouldn't be valid on any unix os
so expand the check.

The check for Windows XP is removed as that platform is not supported
anymore.

When saving a wad for the second time some code would run that tried to
use native windows function and caused a crash.

- A new "Show Textures" option up on the top bar, which draws any sector not flagged to be hidden on the textured automap
- Holding Shift will highlight sectors instead of lines
- Left-clicking on a highlighted sector will toggle the "Not shown on textured automap" flag
- Textures will be shown when Shift is held down even if the "Show Textures" toggle is off

EDGE Classic Game Configuration: fixed a problem with lighting effects in the generalized sector options. Fixes #875

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

Fix mono build on linux

See merge request STJr/UltimateZoneBuilder!1

UDBScript: fixed a problem where floating point default script option values would be converted to the system's locale on hot reloading. Fixes #858

Nodes Viewer Mode: fixed a problem where trying to engage the mode with an empty map could crash. Fixes #857

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

Thing Edit Form (UDMF): fixed a problem where setting floating point values for health wasn't possible. Fixes #225

Stair Sector Builder Mode: fixed an issue where the number of sectors and the sector depth was not loaded correctly when a default prefab was set. Fixes #847