Extend configuration UI by showing the version history of the workspace branch

[mariusoe]

Currently, there is no way to display the version history of the workspace branch of the configuration server in its web UI. However, it is often helpful to be able to view old changes or to know when something was changed.

In order to provide users with the ability to track changes, the Configuration UI should be extended by a history sidepanel in this ticket. In the "configuration view" of the user interface, a sidepanel is to be built in, which will display the versions (corresponding to commits in the local repository). It should be displayed when a new version was created, including its author.
The panel should be expandable and collapsible. If a configuration file is currently selected, all versions in which the selected file was modified should be highlighted.

In this ticket the versions should only be displayed and not allow any interaction.

It can be assumed that the configuration server provides a similar model for fetching version informations like the following:

[
  {
    'name': 'Version 10',
    'id': 'xxxxxxx', # commit id
    'date': 13456789, # timestamp of the commit
    'author': 'admin', # author of the commit
    'changes': [ # modified files
      '/test1.yml',
      '/git/file.yml'
    ]
  },
   {
    'name': 'Version 9',
    'id': 'xxxxxxx', 
    'date': 13456789,
    'author': 'admin',
    'changes': [
      '/test1.yml'
    ]
  },
  ...
]

[mariusoe]

closed by #896