MultiDomain Traits define types inconsistently as const

Some of the types are tuples of shared_ptrs to const types, some to non-const types. This way done in an inconsistent way.

I propose to change it as follows

• Do not provide any tuple types, as we already have MakeTuple (could be renamed to simply Tuple)
• Provide only subdomain types with template arugment size_t i
• Provide other helpers that create a TupleOfSharedPtr and TupleOfSharedPtrConst

This is necessary to implement !1350 (merged).

@kweis, @DennisGlaeser