Add `select` method to Mapdl

[germa89]

It will be nice to have something like:

mapdl.select("KP", [1,2,3])
mapdl.select("NODE", [2, 5, 10])
mapdl.select("COMP", ["component1", "component2"])

I think it will simplify plenty of inner workings and could help developers to speed up their work.