Merge pull request #158 from Blue-Shadow/master

Added GetActorPowerupTics function to the ACS language configuration.
Fix blank line on line info overlay for hexen format maps
Add ability for MapObjectPropsPanel to hide certain properties

Can hide all flags, triggers and arbitrary properties (by udmf property name)
Merge branch 'master' of https://github.com/sirjuddington/SLADE.git
Add custom properties dialog for lines

Will eventually expand it with more advanced UDMF stuff, and add custom dialogs for other types (except maybe vertices). Also changed the action special dialog to include args and triggers, and split it out to a panel for inclusion on the line properties dialog
Fix a bunch of problems from last commit:

- Linux compilation issues
- Various crashes in the line properties dialog when the game configuration is vanilla doom
- Some linux UI quirks (combo box won't allow dropdown if the list is empty)
Implement 'New Tag' button on line properties dialog
Fix problem with Drawing::drawTextureWithin
Add simple NumberTextCtrl class for numeric input

Also allows '++' and '--' prefixes for increment/decrement (will be used on property panels)
Add custom sector properties dialog, among other things:

- Split out SectorSpecialDialog stuff to SectorSpecialPanel class
- Rework properties panels a bit, now all based on PrefsPanelBase class
- Replace text controls for numbers in SidePropsPanel with NumberTextCtrls
Some improvements to line/sector/3d info overlays

- Show question mark icon instead of missing texture for unknown textures/flats
- Show required textures that are missing in red+bold text on the line info overlay
Fix text wrapping for arg descriptions on ArgsPanel
Use unknown texture icons on side/sector property panels
More changes to missing/unknown textures on overlays

- Add new 'minus' thing icon
- Show minus icon for missing textures on line and 3d info overlays
- Draw unknown/invalid textures as icon only w/red text on line and sector info overlays
ZDoom language configurations update:
- Added CanRaise and Slow actor state keywords/flags.
- Added SlowMonsters skill definitions property, and a missing NightmareFast gameinfo definitions property.