Add GitHub ribbons

[siddhpant]

Closes #24.

Used http://tholman.com/github-corners/ as it's used in some other coala repos and was also suggested in the issue discussion.

[SerekKiri]

LGTM 👍

[jayvdb]

@gitmate-bot rebase

[gitmate-bot]

Hey! I'm GitMate.io! This pull request is being rebased automatically. Please DO NOT push while rebase is in progress or your changes would be lost permanently ⚠️

[gitmate-bot]

Automated rebase with GitMate.io was successful! 🎉

[li-boxuan]

Look nice 👍 Please fix the error per review https://github.com/coala/community/pull/225/files/c525ea296d950c86a3270f74b355baeec3b73781#diff-0b5ab4dd0406d0d20e8fd36568ae9821 to make CI happy :)

[siddhpant]

Done

[li-boxuan]

Almost there 👍

[li-boxuan]

LGTM 👍

[TravisBuddy]

Travis tests have failed

Hey @siddhpant,
Please read the following log in order to understand the failure reason.
It'll be awesome if you fix what's wrong and commit the changes.

1st Build

View build log

coala --non-interactive -V

[ERROR][07:14:47] There is a conflict in the version of a dependency you have installed and the requirements of coala. This may be resolved by creating a separate virtual environment for coala or running `pip3 install "git-url-parse~=1.1.0"`. Be aware that the latter solution might break other python packages that depend on the currently installed version.
[INFO][07:14:47] Exception was:
Traceback (most recent call last):

  File "/home/travis/virtualenv/python3.6.3/lib/python3.6/site-packages/coalib/coala_main.py", line 147, in run_coala
    args=args)

  File "/home/travis/virtualenv/python3.6.3/lib/python3.6/site-packages/coalib/settings/ConfigurationGathering.py", line 504, in gather_configuration
    targets=targets,

  File "/home/travis/virtualenv/python3.6.3/lib/python3.6/site-packages/coalib/settings/SectionFilling.py", line 97, in fill_settings
    bear_dirs = section.bear_dirs()

  File "/home/travis/virtualenv/python3.6.3/lib/python3.6/site-packages/coalib/settings/Section.py", line 147, in bear_dirs
    for bear_dir in collect_registered_bears_dirs('coalabears')]

  File "/home/travis/virtualenv/python3.6.3/lib/python3.6/site-packages/coalib/collecting/Collectors.py", line 456, in collect_registered_bears_dirs
    registered_package = ep.load()

  File "/home/travis/virtualenv/python3.6.3/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2404, in load
    self.require(*args, **kwargs)

  File "/home/travis/virtualenv/python3.6.3/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2427, in require
    items = working_set.resolve(reqs, env, installer, extras=self.extras)

  File "/home/travis/virtualenv/python3.6.3/lib/python3.6/site-packages/pkg_resources/__init__.py", line 875, in resolve
    raise VersionConflict(dist, req).with_context(dependent_req)

pkg_resources.VersionConflict: (git-url-parse 1.2.0 (/home/travis/virtualenv/python3.6.3/lib/python3.6/site-packages), Requirement.parse('git-url-parse~=1.1.0'))

TravisBuddy Request Identifier: 685c3730-2c3a-11e9-b3d3-256864349aa7

[siddhpant]

Travis fails due to new version of git-url-parse being available (1.2.0)

#237