add DFN LMSAPI configuration options
DfnDriver: create meetings
add a database table to store meeting for a course
add model class for meetings
[DfnVcDriver] move code to reusable helper methods
pass all parameters to `isMeetingRunning()`
include more user information in the join params
generalise parameters

Move `identifier` and `remoteId` to the base parameter class to make
them available in all parameter classes.
[DfnVcDriver] implemented isMeetingRunning()
[DfnVcDriver] getJoinMeetingUrl() implementation
add a driver factory
add config option to select the default driver
add method to retrieve the default driver
use the driver factory to retrieve drivers
make drivers aware of their internal name
store meetings in the database
there could be more than one running meeting
fix parameters order
create a full JoinParameters instance
display the list of running meetings