This is the first step (the hardest part):
* repo file list last commit message lazy load
* admin server status monitor
* watch/unwatch (normal page, watchers page)
* star/unstar (normal page, watchers page)
* project view, delete column
* workflow dispatch, switch the branch
* commit page: load branches and tags referencing this commit
The legacy "data-redirect" attribute is removed, it only makes the page
reload (sometimes using an incorrect link).
Also did cleanup for some devtest pages.
Introduce RequestContext: is a short-lived context that is used to store
request-specific data.
RequestContext could be used to clean form tmp files, close context git
repo, and do some tracing in the future.
Then a lot of legacy code could be removed or improved. For example:
most `ctx.Repo.GitRepo.Close()` could be removed because the git repo
could be closed when the request is done.
