Index page to root in navigation

Link "Index" page to `./` instead of `./index`
Fix error level and bugs

Set error level in `page.php` to 2 (warnings and errors) and use `isset`
in `sidebar.php`
Update meta

Update meta to something that makes sense
Custom page templates

Looks for `before.html` and `after.html` in `themes/[page]` before using
the generic `themes/`.