fix duplications in enrolled/invited student list

also show different button label between enrolled and invited.
LabsterUserLicense, to store user's license for labs
always create LabsterUserLicense
license overview in dashboard
license overview display in dashboard
Merge branch 'labster/master' of github.com:bodekaer/Labster.EdX into labster/master
move few fields to course_module. add labster_license field (boolean).
admin for LabsterUerLicense
class method to get number of licenses a couse is using
set labster_license field to True when duplicating course via API
fix missing import
new view to get number of licenses a course have
pass course licenses list url to instructor dashboard
update course overview in main dashboard to show the number correctly
delete license data on enroll
update course list licenses to use correct value
display license detail in instructor dashboard
Merge branch 'labster/master' of github.com:bodekaer/Labster.EdX into labster/master