Remove obsolete modules

[uvchik]

• I remove the obsolete and unsed modules
• fixed some tests
• moved the content of __initi__.py to connect.py

[uvchik]

@henhuy The doctests of the results module fail. I disabled them to get a working start point but you should enable and fix them.

[codecov-commenter]

Codecov Report

Merging #39 into dev will increase coverage by 46.59%.
The diff coverage is 80.95%.

@@            Coverage Diff             @@
##             dev      #39       +/-   ##
==========================================
+ Coverage   7.95%   54.54%   +46.59%     
==========================================
  Files          8        6        -2     
  Lines        415      264      -151     
  Branches      52       31       -21     
==========================================
+ Hits          33      144      +111     
+ Misses       381      118      -263     
- Partials       1        2        +1     

Impacted Files	Coverage Δ
src/oemof/db/results.py	0.00% <0.00%> (ø)
src/oemof/db/connect.py	35.71% <35.71%> (ø)
src/oemof/db/__init__.py	100.00% <100.00%> (+64.28%)	⬆️
src/oemof/db/config.py	92.59% <100.00%> (+67.59%)	⬆️
tests/config_tests.py	100.00% <100.00%> (ø)
tests/import_tests.py	100.00% <100.00%> (ø)

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[uvchik]

I do not like the structure of config.py but nevertheless, I added some tests. If we find some time we should revise this module....