The normal go get protocol is to show the go-import meta tag when ?go-get=1 is appended to the url. This commit implements that behaviour and cleans the go-get option from the repository settings page.

Conflicts:
	modules/setting/setting.go

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

Conflicts:
	routers/repo/setting.go