[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