feat(sdk): remove pycrypto and general package cleanup

[Anton0]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

• remove pycrypto since it's redundant "Cannot load native module 'Crypto.Hash._SHA256'" within Lambda Python3.7 #60
• cleanup deps in general
• unit test now installs from setup.py so we're testing dependancies

What is the current behavior? (You can also link to an open issue here)

• install pycrypto (in setup.py and requirements.txt)
• requirements.txt is both dev deps and a duplicate of setup.py

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

• no - if anything it reduces the number of packages users will be pulling down.

[codecov]

Codecov Report

Merging #61 (02694ef) into master (086b52c) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master       #61   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            7         7           
  Lines          329       329           
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  Hits           329       329