First batch of fixes.

- permissionTo is no more. Overall Auth::user() method calls are done with
onAuthUser for now on.
- inputNonEmpty will escape its result, unless it's resulting the default
value. For non-escaped input, the static method Input::get should be used.
- Added a page for maintenance mode (check
app/views/blog/maintenance.blade.php).
- With escaped input body, comments are now being processed to generate
paragraph elements out of line separators.