Add data manager

[mmaelicke]

The DataManager is a wrapper around all data sources used by RUINSapp. It can be configures by any Config class and organizes or caches all data sources using a DataSource inherited class. This makes the read and filter interface available on all sources, no matter where they are stored.
Using the Config to instantiate a data manager can in principle enable different profiles, or even an interaction with the frontend, although not implemented nor desired at the current stage.

Example

from ruins import core

# create default config
conf = core.Config()

# create a data manager from this
dm = core.DataManager(**conf)

Of course, the data manager can also be used without the config, ie. to open it in debug mode:

# using conf with conf.debug=False and overwrite it
dm = core.DataManager(**conf, debug=True)

Review and merge after #18 was merged successfully.
Closes #12

[codecov]

Codecov Report

Merging #23 (29593a0) into main (7d117cf) will increase coverage by 13.54%.
The diff coverage is 75.51%.

@@            Coverage Diff             @@
##            main      #23       +/-   ##
==========================================
+ Coverage   7.92%   21.47%   +13.54%     
==========================================
  Files          4        5        +1     
  Lines        391      489       +98     
==========================================
+ Hits          31      105       +74     
- Misses       360      384       +24     

Impacted Files	Coverage Δ
ruins/core/data_manager.py	75.51% <75.51%> (ø)

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