Add tagging support

[victorlian]

Feature request:

Add support for tagging commits in the past and/or the current commit that has yet to be pushed. This will allow users to mark important points in their repository for example "v1.0" without needing to search for a certain commit message/checksum. Users should also be able to view the tags on the main page.

[lucyJiang279]

After spending two days on this, I have come up with the following. There are many components to this issue:

• Adding support for viewing existing tags which includes display and loading tags in when the graph is loaded
• Adding the ability to view existing commits which includes the same tasks as above
• Adding the UI and backend capabilities for selecting past commits and adding a tag. This also requires that the list of tags displayed is updated
• Adding the UI and backend capabilities for tagging the current commit and updating the list of tags. Therefore I believe this should be at least a large if not very large issue

[lucyJiang279]

I've managed to create a panel for viewing past commits and can populate it with data. However, I have not been able to populate it with commit data from the graphing.ts class. Currently it looks like the only way to do it is to directly modify the html as done with displaying repositories and branches, which I don't have the capabilities to do.