mod_admin_modules: Add "configure" button on module manager

When a module contains a template called _admin_configure_module.tpl, a
button will show on which you can set configuration options for the
module. Implemented currently only in mod_l10n.

(cherry picked from commit 866ca7fff1e8d46aa670b60266f90d378736acd3)

Conflicts:
	modules/mod_l10n/templates/admin_l10n.tpl