[#209] Allows cloning from header.

[Excaleo]

Fixes #209.

Notable changes made in this PR:

• Authenticate.ts has been removed as everything is now decoupled from it.
• With help from @hybrio repopulation of the clone list was done.
• Cloning is now enabled from the toolbar.

Notes:

• Currently the repo is cloned to the current directory due to synchronisation issues with the file picker.
• The visible indicator for selection is in the clone button at the bottom.

To test the functionality in this PR:

1. Login
2. Click on repository in the header. You should see a list of all your repositories.
3. Click any one of them and the clone button should update with the name of the repo you are cloning.
4. Click clone and the repo should clone in the current directory and switch to the main panel.

[qw]

LGTM.

Regarding the error mentioned by @shurui-li

macOS gets this strange error VM261 index.html:1 Uncaught TypeError: $(...).tooltip is not a function When the repository in the header is clicked.

This error is due to the onmouseover attribute calling $(this).tooltip('show'). I think the onmouseover attribute can be removed along with its function call.

I tried that, didn't work. Also weird that $(this).tooltip('show') works for the other header buttons.

@gnawf also has the same issue.