Fix broken login plugins order config handling

The administrative page for configuring login plugins order had
a number of problems.  The html template expects a list of plugin
names to be supplied,  but a list of the actual plugin objects
was being supplied.  This caused a 500 error since join() would
throw an exception when it encounters something other than a string.

Even after fixing the 500 error, actually modifying the plugin
order would not work due to further issues with plugin objects
being used when strings representing the plugin names are expected
(and vice-versa).

This patch ensures that strings representing plugin names are
supplied to the html template, and that plugin objects are used
when re-ordering the live plugin list.

Resolves: https://fedorahosted.org/ipsilon/ticket/2

Signed-off-by: Nathan Kinder <nkinder@redhat.com>
Reviewed-by: Simo Sorce <simo@redhat.com>