pyaeroval: splitting of pyaerocom/aeroval and pyaerocom

[lewisblake]

Is your feature request related to a problem? Please describe.
pyaerocom contains two distinct functionalities which should be maintained in their own repositiorites. pyaerocom/aeroval should become it's own subpackage and then moved into it's own repo.

Describe the solution you would like to see
A clear and concise description of what you want to happen.

Short term: pyaerocom/aeroval (pyaeroval) installed as it's own package in the same repo as pyaerocom.
Long term: moving of pyaeroval into it's own repo as an installable package which has pyaerocom as a dependency

• Would you be able to work on this solution yourself?
  Team work is probably better, but can spearhead this.
• How can the Pyaerocom development team assist you?
  Planning, help with packaging.

Additional context
Part of #772

[lewisblake]

blocked by #1193

[heikoklein]

blocked by #1270