Add a *How to write proper commit messages* section to the our
contributing file which include the git-cop current configuration.

We are using `dist` tag but is not in our contributing file.

Running git-cop to check if the last commits are properly written.

git-cop configuration file has to be copied in:
`~/.config/git-cop/configuration.yml`

The enabled cops with error severity are:

- `commit_author_email`: Ensures author email address exists.

- `commit_body_leading_line`: Ensures there is blank line between the
  commit subject and body.

- `commit_subject_prefix`: Ensure that the commit has one or more tags
  (*api*, *app*, *backend*, *ci*, *dist*, *doc*, *webui*)
  alphabetically ordered.

The enabled cops with warning severity (a message is render when
executing git-cop but it doesn't fail) are:

- `commit_body_bullet`: enforce `-` for lists.

- `commit_body_line_length`:  Ensures each line of the commit body is
  not longer than 72 characters.

- `commit_body_phrase`: Avoid meaningless words/phrases.

- `commit_body_presence`: Ensures the commit has a description.

- `commit_subject_length`: Ensures the commit subject length is not more
  than 50 characters.

This gem will help us to write better commits.

Update airbrake to version 6.2.1

Update timecop to version 0.9.1

Update haml to version 5.0.2

Update acts_as_list to version 0.9.7

Update capybara_minitest_spec to version 1.0.6

[frontend] Bugfix writing to backend

[api] SourceController#project_command_release uses ActiveJob

[api] BsRequest.delayed_auto_accept uses ActiveJob

Refactoring ProjectStatus::PackInfo and ProjectStatus::Calculator

[webui] Help the user to introduce valid kiwi data

Add help and error messages in the kiwi repository and package dialog.
Any error was before rendered until clicking the Save button, which is
confusing and annoying for the user.

Pair-programmed by @DavidKang and @Ana06.

instead of setting links_to attribute to id and overwritting it later with the actual PackInfo object.

and delegate to the backend_package instead.
Introduced parsing to_i in setversrel function as
JobHistory will input an integer to this function
but backend_package returns a Time object.

and dropped unnecessary AS and added whitespace.

Drop the link calculation as it was broken and did not work anyway.
- package.project set after it was checked in the condition -> never true
- Even the condition would have been true, package.links_to_id fails as PackInfo
  does not contain this attribute

[webui] Change place of kiwi save button

Update faker to version 1.8.4

[webui] Add order to repository

[dist] Drop superflous common.sh from Vagrant

[ci] Fix depfu branch exclusion regex...

[webui] Fix editor haml view

Update capybara to version 2.14.4