Fix and use use_login_page for the BlockIP pre-rendered page (#79)

Fix and use use_login_page for the BlockIP pre-rendered page (#79)

* template/en/default: Fix use_login_page

The implementation fell off in
2e5d910d9401c4fa8f105d8f9502d9e4ea27bb99.

* template/en/default/global/ip-blocked.html.tmpl: Use use_login_page

This fixes the warning "Use of uninitialized value $args[1] in join or
string at .../Bugzilla/Token.pm line 270", and removes the
likely-broken mini login form on the "IP blocked" page.

* index.cgi: Disable use_login_page for the front page

This seems to be only useful for very high-traffic
installations (BMO).

Co-authored-by: Dylan Hardison <dylan@hardison.net>