Replace submission plugin section header with label

Signed-off-by: Tony Butler <tonyjbutler@gmail.com>
Fix invalid argument errors if user has no Mahara account

Signed-off-by: Tony Butler <tonyjbutler@gmail.com>
Add support for new Moodle activity logging events API

Signed-off-by: Tony Butler <tonyjbutler@gmail.com>
Bump version number and require Moodle 2.7

Signed-off-by: Tony Butler <tonyjbutler@gmail.com>