Merge pull request #72 from Gaerzi/master

Don't collect objects with id 0.
Only draw thing paths when in things mode
Optimised MapSector::getColour, should be a noticable improvement for large ZDoom+UDMF maps such as ZDCMP2
Changes to the thing path stuff:
- Don't calculate paths every time renderPathedThings is called
- Dragon path stuff disabled for now
(paths should probably be calculated elsewhere - maybe in MapEditor, and only updated/recalculated when needed, as calculating them every frame is very slow, especially noticable in ZDCMP2)
Merge branch 'master' of https://github.com/sirjuddington/SLADE.git
Eliminate redundant CHR() macros.

See http://docs.wxwidgets.org/trunk/classwx_string.html#string_vararg
for explanation about how it is not needed for wxFunctions like
String::Format or wxLogMessage.

Also changed CHR's C-style cast to a safer static_cast.
Merge branch 'master' of https://github.com/sirjuddington/SLADE