Closes #42 by implementing drag/drop functionality

[TAFrew]

This pull request implements drag and drop functionality for staging and unstaging files (Closes #42)

Users can drag files from the unstaged section of files into the stage section which will stage the file on drop, as opposed to the old workflow where files were staged the moment the user clicks on commit.

There are also buttons to stage all files and the unstage all files, providing multiple ways for users to stage and unstage files.

In our design and implementation, we thought it would be preferable for the real "staging and unstaging" of files to be implemented so that the feature would seem as complete as possible. Due to this functionality already existing as an issue (#33) and taken by another team, we have coordinated with them in delivering our feature. We have been blocked in waiting for the back-end staging to be implemented so that we can integrate it with the new drag/drop front-end.

[softeng-701]

@TAFrew Please squash your commits. You must have 1 or 2 commits to be merged, thanks!

[TAFrew]

@softeng-701 squashed commits

[kdhira]

I have removed the dubugging lines

[kdhira]

@softeng-701 Changes were made, but now approved and ready for merge

[softeng-701]

@TAFrew Looks good, will merge after the deadline