Pip install fix

[Chilipp]

• Closes Installation with pip and Qt #1, Tests abort on MacOS #8
• Tests passed (for all non-documentation changes)

[codecov]

Codecov Report

Merging #6 into master will increase coverage by 2.06%.
The diff coverage is 87.77%.

@@            Coverage Diff             @@
##           master       #6      +/-   ##
==========================================
+ Coverage   86.11%   88.17%   +2.06%     
==========================================
  Files          26       26              
  Lines       11247    11313      +66     
==========================================
+ Hits         9685     9975     +290     
+ Misses       1562     1338     -224

Impacted Files	Coverage Δ
straditize/widgets/colnames.py	88.16% <0%> (+22.33%)	⬆️
straditize/__main__.py	80% <100%> (-2.8%)	⬇️
straditize/colnames.py	91.33% <100%> (+43.38%)	⬆️
straditize/widgets/data.py	91.63% <100%> (ø)	⬆️
straditize/binary.py	88.03% <100%> (+0.12%)	⬆️
straditize/widgets/menu_actions.py	74.45% <50%> (-0.11%)	⬇️
straditize/magnifier.py	93.06% <76.47%> (+1.4%)	⬆️
straditize/widgets/tutorial/beginner.py	94.09% <87.5%> (+0.03%)	⬆️
straditize/straditizer.py	89% <92.59%> (-0.8%)	⬇️
... and 5 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 07f1696...0e9f8af. Read the comment docs.

[Chilipp]

This PR is ready to be merged. It addresses #1 and #8. In particular:

• it adds pyqt5 to the dependencies in setup.py (see Installation with pip and Qt #1)
• it adds tests for the installation with pip in .travis.yml (see a561cba and 892faba)
• it changed the installation instructions for the installation from source (see the docs and README and the installation with conda
• it resolves several memory leaks in the test suite (although there are still some) and improves the instructions on running the tests (see the docs)

It will be merged if @sgrieve and @ixjlyons are okay with the proposed changes (see #1 (comment) and #8 (comment)).

[ixjlyons]

I added a few nitpick comments, but installation with pip works and it looks good to me. I didn't look closely at the testing related changes but I'm assuming CI is more thoroughly checking all that :)

[Chilipp]

Thanks a lot for your quick response and your time! The suggested changes have been implemented. I will merge this PR now.