Add functionality for managing issues (Issue #37)

[bpar476]

There is a new "issues" menu on the right hand side of the application that updates when your repository changes as well as periodically updates to see if issues have been created since.

Users can view, create, close and comment on issues. Uses the octonode github api.

Fixes #37

[bpar476]

@softeng-701 This branch has over 20 commits and I've spent many hours doing this. There are loads of commits inbetween mine so there is no easy way for me to squash them on my end without completely re-writing the repository history. I can try if you are sure that you want the commits squashed manually, otherwise I would suggest just using githubs "squash and merge" feature to automatically and safely squash these commits together.

[softeng-701]

@bpar476 yes please squash your commits as best you can, its part of the assignment to do this. You can ignore commits that aren't your own and merge commits

[bpar476]

Created PR from a new branch with squashed commits. See here: #176