Remove unused CSRF options, decouple "new csrf protector" and "prepare"
logic, do not redirect to home page if CSRF validation falis (it
shouldn't happen in daily usage, if it happens, redirecting to home
doesn't help either but just makes the problem more complex for "fetch")
(cherry picked from commit 1fede04b83288d8a91304a83b7601699bb5cba04)
Conflicts:
options/locale/locale_en-US.ini
tests/integration/repo_branch_test.go
trivial context conflicts
