Feat: ability to reset to a remote meta ref

[Ramdek]

Context

While trying to allow unauthenticated users to only create new ticgit issues on a repository, it seems that ti lacks the ability to compare and reset with a remote meta ref.

Feature ideas

ti diff

Show differences between local and remote ticgit db.

This is currently possible with git's plumbing command diff-tree just like ticgit's commit messages.

ti reset

Reset local db state to a remote state.