[PL] GW: Store hydraulic conductivity in each elem.

This shall be changed later to incorporate different
material properties.
[PL] Add GlobalSetup as template to GW process.

Enable parsing of processes' configs, now the types are correct.
[PL] Add global matrix and rhs/solution vectors.
[PL] GW: Add LinearSolver.

Make linear solver happy with identity matrix for now. Will be removed after
local assemblers are called.
[PL] GW: Add vector of local assemblers and initialization.
[ML] Remove size check, because eigen has no getNRows()

Maybe we should choose different interface instead.
[PL] GW: Add global assembler.
[PL] GW: Execute global assembler on local assemblers.
[PL] GW: Add debug messages in init, solve, post.