Expose IsLocked Property

* Fix panic in API pulls when headbranch does not exist
* refix other reference to plumbing.ErrReferenceNotFound

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Display pull request head branch even the branch deleted or repository deleted

* Merge getHeadRepo/loadHeadRepo and getBaseRepo/loadBaseRepo on pull and fill repo when pr.Issue.Repo is available

* retrieve sha from pull head when pull request branch deleted and fix tests

* Fix test

* Ensure MustHeadRepoName returns empty string if no head repo

Co-authored-by: zeripath <art27@cantab.net>

* Label: delete .APIFormat() and use convert.ToLabel()

* move issue APIFormat too

* add missing one

* move TEST too

* handle error -> return empty APIIssue

* Apply suggestions from code review

Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>

Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: guillep2k <18600385+guillep2k@users.noreply.github.com>

* only try to get HeadBranch if HeadRepo exist

* impruve

* no nil error

* add TEST

* correct error msg

* Move newbranch to standalone package

* move branch functions to modules to avoid dependencies cycles

* fix tests

* fix lint

* fix lint

* Move pull request api convert to convert package

* Rename ToPullRequest to ToAPIPullRequest