Support data writing with meshConnectivity

[davidscn]

This issue refers to PR #46 , which adds a support for nearest-projection mappings (#2 )

Our current workflow looks the following way (for nearest-projection):
Writing:
compute_data -> interpolate from centers to nodes -> write data to the buffer
Reading:
get read data -> apply data on cell centers

We decided NOT to perform the reading like:
get read data -> interpolate from nodes to centers -> apply data on cell centers
since the interpolation can be done by precice, if we configure additionally a Fluid-Centers mesh and let precice write on this mesh.

However, for the user, it would be much easier to have both options. If you don't care about performance and just want to calculate a small case for example. Then you just set up locationsType = faceNodes and provideMeshConnectivity = true, respectively in the precice-config.xml, and you are done. This would require to add the interpolation additionally in the read() functions of each data class (reverse direction as already implemented in the write() functions).

Additionally: The read() workflow is just implemented in the CHTclass, since the FSI class usually doesn't need to provide connectivity (have a look in the NP tutorial for details). Still, it might be of interest for a general implementation of the adapter.