Visual mode, UDMF: we shouldn't render fade when sector brightness is 248 or higher.

Plugins: fixed a crash caused by inability to find referenced assembly when loading a plugin, which depends on other plugin(s).
Undo-redo, UDMF: undo information was not created properly for several types of UDMF fields for the last map element in the selection when the selection contained more that 1 element.
Updated documentation.

Maintenance stuff:
Core/Plugins/Plug: made current display location and size information properly available to plugins.
Made Core/Controls/ColorControl available to be used by plugins.