This is now replaced with the more capable and correct `Stack` trait, implemented on `Branch`.
The new endpoints are:
create_series,
remove_series,
update_series_name,
update_series_description,
push_stack,
- The PatchReference type represents a "reference" that is entirely managed by GitButler. It can either point to a commit or a GitButler change (which itself points to a commit)
- The Branch type (as persisted in virtual_branches.toml) now has a `heads` fields with a list of PatchReferences. This list is not to be meant to be manipulated directly, but with the `Stack` trait
This is more descriptive to what logic lives inside. Further, this allows for splitting up the just branch bits in a separate crate (which is currently in gitbutler-core)
This protects us from cyclic dependencies. Unfortunatelly as part of this, i had to introduce the imp Project as trait implementations since now Project is foreign
We want to move towards having each functional domain in a separate crate.
The main benefit of that for our project is that this will enforce a unidirectional dependency graph (i.e. no cycles).
Starting off with virutal_branches - a lot of the implementation is still in core (i.e. virtual.rs), that will be moved in a separate PR.
Furthermore, the virtual branches controller (as well as virtual.rs) contain functions not directly related to branches (e.g. commit reordering etc). That will be furthe separate in a crate.
