Updated popup function

The function no longer uses the duplication method.

Duplication method is where the function clones the desired contents
into the popup holder whenever a popup is being shown.

It has now reverted back to the old method, where the desired popups are
all shifted into the main popup holder, and are then simply shown/hidden
as required.
Completely refactored Validify function

- Updated the function to use the new plugin structure.

- Instead of using custom event handlers, the plugin now uses methods
added onto the elements themselves to carry out any function needed. For
example, you can call $('form').data('validify').updateStatus() to force
all fields in the form to validate themselves, and then you can check
$('form').data('validify').status to determine whether or not the form
has passed validation.
Update Popups function & docs

- Function is no longer able to programmatically adjust the popup
heights. This forces us to use CSS only, which is a way of standardising
it.

- Optimised/Fixed some stuff in the codes

- Updated the docs to reflect the latest function changes
Removed outline from nav toggler
Updated Dropdown function & docs

- Dropdown function has been optimised a little
- Dropdown function will now check for its required elements first. It
will only create the elements if it can't find them.
- Docs updated to reflect the changes.
Updated Validify function & docs

- Validify function now has `destroy` methods. Need to test it first
though.
- Renamed one of the function to be less ambiguous.
- Updated docs to reflect latest changes. Still incomplete, however.