MAKE: refactor Makefile

improved readability, moved tools at the top, rules at the bottom

make -> build core
make all -> build core and tools
install -> install core
install-all install core and tools
MAKE: revert DATA_INSTALL_DIR value for backwardscompat

otherwise build scripts will have to adjust
MAKE: simplify install rules

just copy all mod folders recursively, this also fixes
missing d2k/weapons and ra/sequences folders
MAKE: install more missing files

this should fix crash when clicking on "credits"
and the asset browser
MAKE: quote all variables that can contain whitespace
Merge pull request #3500 from hasufell/Makefile

MAKE: refactor Makefile