Fix some problems with the thing properties panel

- Actually apply special/args values
- Fix crash on applying changes (Fix #163)
- Fix crash on opening properties for multiple things
Replace opengl thing direction chooser with custom control

Couldn't get the opengl canvas to behave correctly in linux/osx for some reason. No fancy arrow but might add it back later
Fix potential crash in thing properties panel
Bump version to beta 5
ZDoom language configurations update
- ACS:
  - Added STYLE_AddStencil and STYLE_AddShaded constants.
  - Added ChangeActorAngle and ChangeActorPitch functions.
  - A minor fix in SetActivator syntax.
- DECORATE:
  - Added AddStencil and AddShaded render styles.
  - Added CHAN_* and SPF_INTERPOLATE constants.
  - Added "flags" parameter for A_SetAngle.
- MAPINFO: Added DontCrunchCorpses flag for gameinfo block.
Merge pull request #165 from Blue-Shadow/master

ZDoom language configurations update
Merge branch 'master' of https://github.com/sirjuddington/SLADE into osx