[Python|OGSMesh] Add required functionality and fix bug outputting every time step

• Add functions to access
  • the names of all available data arrays / PropertyVectors
  • the number of components of a data array / PropertyVector
  • the mesh item type of a data array / PropertyVector (Node or Cell)
• Move outputting the results of the last time step into function finalize() of the Python interface (fixes output bug)

API Overview

from ogs import OGSMesh, OGSSimulation  # Python API to a running OGS

OGSSimulation:

• __init__() # statt initialize()
• current_time()
• end_time()
• execute_time_step()
• mesh() # statt getMesh()
• mesh_names() # neu
• close()
• def exit(self, exc_type, exc_val, exc_tb): self.close()
• def enter(self): return self

OGSMesh:

• mesh_item_type()
• data_array_names() # statt getDataArrayNames()
• data_array()

~~ - getNumberOfComponent()~~ ~~ - materialIDs() ~~

1. Feature description was added to the changelog
2. Tests covering your feature were added?
3. Any new feature or behaviour change was documented?