Rework the mysql::bindings to be less complex.

This removes all the internal class parameters and shrinks these classes
to be more straightforward, relying on the values set in bindings.pp.
Various adjustments to classes to align with refactored work.

Handful of changes here, such as removing flush (so that mysql_user
can be used for root password changes) and other tweaks here.

Add time option to mysql::backup.
Rework templates to rely on the new hash and become vastly less complex.
Rework the documentation to align with the new refactored module.
Rewrite spec tests to account for changes.