branch based git integration

[RealJohnSmith]

Keep information about time spent on HEADs of different branches -> when checking out branch, time spent also checks out and IDE will keep updating new time in new branch. Same thing for stack-ed commits.

[RealJohnSmith]

And when applying from stack, it should add the stack time to branch time, not replace it (as checking out branches should do)

[Darkyenus]

post-checkout hook could be used to implement this (not stash, as it has no hooks). But I am not sure if this can be done intuitively. Binding tracked time to some task system like proposed in #9 seems easier.