MDL-23234 finally standardised use of settings.php across all plugins - the only partial exceptions now are report and local plugins

This hack allows auth plugins to migrate to the new auth_xxx naming
style (as happened with auth_mnet in my previous commit).

 - response files uploading now uses the new file manager element in advanced upload type. (@TODO: single upload->use file picker)
 - fixed file manager using $USER->id, now using the submission->userid to display the file area files.

MDL-22952 (bulk commit) - Fixed bidirectional page problems (right to left). Add new images for navigation.

rating MDL-22283 rating_manager::get_user_grades() was only expected a single user. When you alter the forum grade settings get_user_grades() is called with user id 0 meaning all users. Updated it to handle this.

enrol MDL-23232 Added missing caps and plugins checks and copied both sets from the manager to implementing scripts

MDL-23182 - Removed use of tabs. Added in PAGE functions and parameters so that nav menu will appear properly. Changed use of 'course' parameter to 'courseid' parameter to be more accurate.

MDL-23232 added support for enrol_plugin->all_enrol()  which indicates plugin allows users to add new enrolments manually

There is no need to have whole featured theme selector with previews
etc here. Following the same form element as they have in Mahara, the
theme can now be selected for a given peer at 'Review host details' tab.
I have also noticed that force_theme and theme columns are redundant at
the moment. Keeping them both for future improvements, though.

Double slashes and eventual whitespace after trailing slash are now
removed, too.