History interface should have a 'fork' or tag button

[nsheff]

1. interface should have a 'fork' or tag button

Right now, when viewing history, I can either Restore or Download

What I really want to do is fork this into a new tag. Using the same repo name but just add a tag.

Maybe equivalently, and interface to "add a tag" to a history entry.

2. Move exit to right side

I find it unintuitive that the exit button is on the left. I guess because I'm used to exit buttons on windows always being in the top right. I would find it clearer to move Exit to the top right.

[sanghoonio]

method: fork the current project with its history (copy over if not preserved) to create a new pep. apply selected history point to forked pep, then erase the history in the forked pep