Rollback screen improvements

[mt-bt]

Love the feature, here are some things I wish I could do from the rollback screen:

• Being able to see the commit of each image (similar to what we see in the deployments page), right now the SHA is not that helpful
• Remove older images manually in a simple click

[ksaitor]

• Move Rollback functionality from Configuration to Deployments tab
• In Configuration -> Rollback, users should be able to config number of containers to keep at any time, for instant rollback

Rollback button example:

[ksaitor]

Looks like no one has looked at this issue. Very UI simple fix, imho. But big UX improvement.
Also, "Rollback" actions are currently under "Configuration" tab, yet there is no rollback config there at all. Does not make logical sense.

cc @andrasbacsai