Compatibility with preCICE v3

[MakisH]

At some point in the next year, preCICE v3 is coming. We need to update the adapter accordingly.

Changes to consider:

• Drop issue Only write data to the preCICE buffer if required #3
• Merged initializeData into intialize: Merge initializeData() into initialize() precice#1350 -> Solved by Replace actions with explicit calls #266.
• Updated connectivity API (adjust setMeshEdges and setMeshTriangles to use vertex IDs): Vertex-only API precice#1322, Clarify mesh API precice#1321 -> Solved by Mesh connectivity for preCICE v3 #297.
• Updated actions/checkpointing API: replace isActionRequired(action) with explicit calls precice#719 -> Solved by Port the adapter to preCICE v3 #285
• Unsigned sizes: Use unsigned sizes in SolverInterface precice#405
• (additional) Exiting the coupling earlier, if needed: Exit the coupling earlier precice#1118
• Apply any waveform iteration related changes needed. -> Solved by Port the adapter to preCICE v3 #285.