Make the "types" setting optional

[jwodder]

This PR makes the "types" setting in the config default to all event types if it is not specified.

After this PR is merged, I will remove the "types" setting from config.yml in tinuous-inception so that future PRs like #95 will take effect automatically without the need to edit tinuous-inception.

[jwodder]

The tinuous-inception test failures are because #95 hasn't been merged yet.

[codecov-commenter]

Codecov Report

Merging #96 (210dba8) into master (0f13cf6) will decrease coverage by 27.11%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           master      #96       +/-   ##
===========================================
- Coverage   67.92%   40.80%   -27.12%     
===========================================
  Files           9        8        -1     
  Lines         820      816        -4     
  Branches      121      122        +1     
===========================================
- Hits          557      333      -224     
- Misses        221      482      +261     
+ Partials       42        1       -41     

Impacted Files	Coverage Δ
src/tinuous/config.py	75.94% <0.00%> (-15.19%)	⬇️
src/tinuous/__main__.py	0.00% <0.00%> (-58.65%)	⬇️
src/tinuous/appveyor.py	33.33% <0.00%> (-46.92%)	⬇️
src/tinuous/base.py	61.60% <0.00%> (-26.40%)	⬇️
src/tinuous/github.py	31.12% <0.00%> (-22.45%)	⬇️
src/tinuous/travis.py	28.97% <0.00%> (-8.42%)	⬇️
src/tinuous/util.py	79.54% <0.00%> (-6.82%)	⬇️
src/tinuous/_version.py

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[yarikoptic]

Looks lgtm, thank you!