This allows the admin to disable the version information about gogs and
go in use in the footer.

This is because git command line shows the failure reason only if Content-Type is text/plain.

- modules/middleware/context.go: add HandleAPI method

The boolean flags in the repo context have been replaced with mode and two methods

Also, the permissions have been brought more in line with https://help.github.com/articles/permission-levels-for-an-organization-repository/ , Admin Team members are able to change settings of their repositories.

Conflicts:
	modules/setting/setting.go

Conflicts:
	templates/repo/release/list.tmpl
	templates/user/dashboard/dashboard.tmpl

Conflicts:
	routers/repo/setting.go