Merge pull request #1 from throup/master

Non-functional: reformat code to minimise CodeSniffer warnings (Moodle code style).
added blank update scripts
process groups now works when the user is logging into the site
new version number, added group id migration script
reworked group functionality to work with new idnumber mechanism
added setting to control group removal behaviour
check plugin configuration before cleaning up groups
added standard function can_hide_show_instance. I won't ruin the ending for you though
Added build scripts to support development tools (including Moodle coding standards, php documenter). Updated README.md to include instructions for configuring a dev environment.