fix regression from a7f1632dcf8b23b1e937c5feb1718ae91b930083
enable space specific in-templates for cfg extras
enable additional cfg extra files via project specific global variable
modified resolve order for env hooks and cfg extras, first look for specific files than for generic ones
enable cfg extras with absolute path, allow having a cfg extra file for one space and not bail about a missing file for the other space
modified handling of metapackages, they must have a CMakeLists.txt for catkin_make_isolated, catkin_make will generate one on demand and warn about it (#349)
fix sourcing env hooks for specific shells (regression of f8d37d8551c2ccb1f79641615ab9f4ec7d8990d7)