[functions.* and test.functions.*] some renaming
-rename namespace Function to Functions
-rename class Functions to FunctionsProvider
[functions.interfaces.hh] add new GlobalFunctionInterface
[functions.global] mark as deprecated
[functions.constant] Constant now inherits from new GlobalFunctionInterface
[test.functions_constant] remove one test as it is not compatible with the refactoring of Constant
[functions.expression] remove inclusion of deprecated global.hh
[la.container.eigen] remove empty line
[test.test_common] silence warnings
Merge branch 'master' of https://users.dune-project.org/repositories/projects/dune-stuff

Conflicts:
	dune/stuff/functions/constant.hh
[functions.constant] fix error I introduced when manually resolving merge conflict
move functions/fromfile.hh to playground/functions/ and remove associated test
Merge branch 'master' of https://github.com/tobiasleibner/DUNE-Stuff
[functions.interfaces] added missing includes
[test.functions_functions] added try/catch guard