Fix #3899: SkinChooser needs a moveable divider

Also let it highlight the currently active skin when opening the dialog.
Fix #3900: Prefab Selector showing non-prefab files, plus attempts to open folders
Merge branch 'master' of https://github.com/orbweaver/DarkRadiant
Set Fit Texture entry box digits to 2 in SurfaceInspector.
Fix #3851: sound shader parser ignores sound file paths with backslashes
Mark TransientWindows as tool windows, this resolves a few minimize issues in Windows.
Add default filter excluding func_static entities.
Display a text control next to the colour picker in the ColourPropertyEditor.
Colorize the playback control button images.
Include two new script commands PatchSplitter and ASE Blend Export.

by request of Bikerdude
Compilation fix for Linux.
Increase scrolling speed in LayerControlDialog.
Add global filter for key events for better shortcut handling. Treeview typeahead is broken at the moment.
Event handling now working with wxutil::TreeViews too.
Update comments, smaller methods.
Remove EventManager::connect/disconnect method pair and KeyEventPropagator. Linux build needs to be checked.
Try to fix the EntityInspector type error in wxGTK.
Linux build script updates