Push logic:

@unison/base:main> project.push [project:branch]

If not on a branch, bail.

Resolve where to push:
- If project/branch names provided
- If project_id/branch_id in remote_project/remote_project_branch tables
- goto 1 (project_id branch_id)
- else
- if the ids exist on Share
- goto 1 (project_id branch_id)
- else
- create them on Share
- goto 2
- Else project/branch names not provided
- If default push project_id exists
- If default push branch_id exists
- Goto 1
- Else default push branch_id doesn't exist
- If this branch name exists under the default project_id
- goto 1 (project_id, branch_id)
- Else
- create the branch on Share
- Goto 2
- Else default push location doesn't exist
- Get my username
- Do all the logic with the

label 1:
Now we have remote (project_id, branch_id)

label 2:

-- else if (default push location exists),
-- if (its remote branch id is non-null)
-- use that
-- else
-- if (this branch name exists in that project)
-- use that
-- else
-- create a branch with this name
-- else
-- ask Share for my username
-- if (I'm not logged in)
-- fail -- don't know where to push
-- else