De-deprecate controller and view specs

We deprecated controller and view specs on the grounds that they were
brittle, and were a poorer measure of user experience than feature
specs. However, feature specs have their own problems: they're much
slower to run, and flakier (see #901). We also ran into a few cases
where feature specs erroneously passed because they were checking for
the presence of a string that occurred in the error page!

Hence, we're cautiously un-deprecating controller and view specs.

Fixes #1132
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Gitea Version: 1.28.0+dev-477-g8b6ad49a5f