Refactor decoration-related code

Split up ModApiMapgen::l_register_decoration()
Define and make use of CONTAINS() and ARRLEN() macros
Added names colours and refactored parseColorString()
Add option to enable mesh caching, add wallmounted for meshes.
Fix bug introduced by me (Zeno)
Merge remote-tracking branch 'minetest/master'

Conflicts:
	freeminer.conf.example
	src/defaultsettings.cpp
	src/itemdef.cpp
	src/util/numeric.h
	src/util/string.cpp