Cleaned up redundant code (and a typo missed earlier).

Removed redundant declarations and checks in the code.

Ensure previous CSS classes are not appended and reinitialized in the foreach loop.

Used ```Html::addCssClass``` and ```Html::removeCssClass``` more effectively.

Added closeButton parameter, assignment of CSS class corrected, and added php doc comments.

The previous alert widget within the advanced/basic app does not render multiple flash messages. The current implementation allows display of all flash messages assigned through setFlash. Also a validation is done for allowed bootstrap alert types.

Small edit for consistency with /apps/advanced/backend/config/main.php. Sorry, my OCD kicked in.

Modified application templates so when trying to log in when already logged in it just redirects to homepage instead of throwing exceptions