upgrade pipot from python2 to python3

[VertexC]

The change has passed both 2.7 and 3.6 test on travis. As python Enum right now is directly acceptable by the SQLAlchemy Enum type as of SQLAlchemy 1.1, the DeclEnum is removed.

[codecov]

Codecov Report

Merging #30 into master will decrease coverage by 0.68%.
The diff coverage is 90%.

@@            Coverage Diff             @@
##           master      #30      +/-   ##
==========================================
- Coverage    45.4%   44.72%   -0.69%     
==========================================
  Files          23       23              
  Lines        1775     1726      -49     
==========================================
- Hits          806      772      -34     
+ Misses        969      954      -15

Impacted Files	Coverage Δ
database.py	94.44% <ø> (+17.63%)	⬆️
mod_config/controllers.py	35.9% <0%> (ø)	⬆️
config_parser.py	22.22% <0%> (ø)	⬆️
mod_config/models.py	77.14% <100%> (+0.33%)	⬆️
mod_honeypot/controllers.py	22.06% <100%> (ø)	⬆️
mod_honeypot/models.py	62.37% <100%> (+0.37%)	⬆️

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