Forest, Minimal and the site theme: include the password login form #666

Problem

#664 adds password login as a shared partial, _password_login, which the default theme's login.html includes. goblog-theme-forest, goblog-theme-minimal and goblog-site-theme ship their own login.html without it.

A site where a password is the only way to sign in is fine: goblog renders its own login page there, and /login?password=1 always reaches the form. But a site with both GitHub login and a password admin, on one of those themes, shows only the GitHub button.

Fix

In each theme's login.html:

{{ if .password_login_enabled }}{{ template "_password_login" . }}{{ end }}

and raise min_goblog_version to the release that contains #664, since the partial does not exist before it.

Follow-up to #664.