Status: Make various improvements to the Status class

Status: Make various improvements to the Status class

These improvements touches areas such as;
- strict comparison as count() returns in int.
- use of single quotes for string literals.
- use of RequestContext to get the user's Language object.
- fix minor typo.

The todo for using RequestContext was added in 7c543bb6c25.
It used `$wgLang` at the time for consistency with Message.php,
which was changed in 2016 with 0beb5ca992c. Hence, it's now
fine here as well.

Change-Id: I943dfd761a8fca7e8b6658e3c9510ddc6694f042