Unstaged changes can be useful or necessary for some tasks
e.g. absolute emergency (where even faking the state of a staging is
not really desirable, if that's even possible anymore), or changes
which are so broad they're difficult to stage (e.g. t10s updates).
Add a new object which serves as a queue for patch to direct-apply,
with support for either text patches (udiff style out of git show or
format-patch) or commits to cherry-pick. In the former case, the part
of the show / format-patch before the diff itself is used for the
commit metadata (author, committer, dates, message) whereas for the
commit version the commit itself is reused as-is.
Applied patches are simply disabled for traceability.
Fixes#926
