Summary:
Once we have revealed the commits to the user (D22864223 (578207d0dc), D22762800 (f1ef619284)), we need to merge the imported branch into the destination branch (specified by dest-bookmark). To do this, we extract the latest commit of the destination branch, then compare the two commits, if we have merge conflicts. If we have merge conflicts, we inform the user, so they can resolve it. Otherwise, we create a new bonsai having the two commits as parents.
Next step: pushrebase the merge commit
Minor refactor: moved app setup to a separate file for better readability.
Reviewed By: StanislavGlebik
Differential Revision: D23028163
fbshipit-source-id: 7f3e2a67dc089e6bbacbe71b5e4ef5f6eed2a9e1