Instead of deriving from the process-related handle classes the
handle class contains these sub-handles and provides access to it.
That allows process-independent algorithms on the sub-handle classes
as soon as the return functions get more generic names.

Resizing of the matrices place in the local assembler directly wherr
needed. This has a small negative impact on performance but saves a lot of code.

Not providing an overload for a function in the base class within
the interaction volume implementation would have led to an infinite
loop. We now throw if any of the functions are not overloaded.

[gridvars] Unify for stationary and instationary problems

See merge request !1306

[test][1p][quad] add missing namespace specifier

See merge request !1307

[ni] Remove unused alias

See merge request !1305

[test][navierstokesnc] Use different executables for caching on/off

See merge request !1303

Provide a script that replaces property macro usages

Closes #593

See merge request !1300

Feature/user specified solid params in spatial params

Closes #578

See merge request !1231

[propertysystem] include propertysystemmacros.hh again

See merge request !1299

Prevent user code from breaking. Inclusion will be removed after
proper deprecation.

Feature/fvgeometry boundary

See merge request !1290

Replace propertysystem macros

See merge request !1296