popup back button history

[extrawurst]

currently we have no history of where the user comes from when opening the blame/commit-detail popup. would be nice to keep track of that and allow going back to where the user came from.

simple use case:

• go to file tab
• choose a file and open blame
• choose a commit and inspect inside blame
• commit details are open now
• close commit details
• we are back in the file tab

I would expect to be back in the blame popup

[R0nd]

Added popup history and changed popups inside blame and branchlist to use it to pop back

[extrawurst]

example: