Add option to tag revisions

[glogiotatidis]

We can enable users to tag specific revisions to point special points in the timeline of the pad. Easy access to the different tags through intuitive API, API fetch of pads based on tags.

[JohnMcLear]

@glogiotatidis You happy for this to be closed now? Let me know if you feel like we didn't accomplish what you want. We didn't create a UI for it but you have the ability to access REVs through the HTTP API so building it into an app would be relatively simple in theory.

[glogiotatidis]

Unfortunately I don't work on the same project anymore, so I can't verify if that's working or if it gets the job done. Thanks for the followup though and keep up the good job.