Avoid modifying the PATH for the python test suites

[bigspider]

Instead, install the local ledger_bitcoin package as part of the requirements.txt.

Moved all the various requirements.txt to a single file in the root of the repo.

Closes: #307

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.70%. Comparing base (24bcdae) to head (bf12689).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #308   +/-   ##
========================================
  Coverage    84.70%   84.70%           
========================================
  Files           17       17           
  Lines         2230     2230           
========================================
  Hits          1889     1889           
  Misses         341      341           

Flag	Coverage Δ
unittests	84.70% <ø> (ø)

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