fixed some deprecation warnings
Correct icon calling name to avoid broken images on courses list
Make overridden function declarations match their parents declaration
Correct grammar issues
Deprecate unused locallib function - see #3
Update README.md

More information about the current "Maintenance" mode of the plugin.
#4 Update version to 2.2 as using some functions introduced in 2.2 + correct link to the "issue poll" in the readme.md
Update version to 2.2 (correct version number)
Update README.md
Add enrol icon into the enrolment method + remove some whitespaces + remove add some setType
Create enrol_invitation.php

Dutch translation file, should be put in folder 'nl'.
Move contributed nl lang file into new lang/nl folder.