Display notification that max concurrent sessions has been reached (GRN-41) (#317)

* <Added max concurrent sessions check>

* <Refactored some exception logic>

* <Fixed code style>

* <Generalized BBBException error message>

app/models/room.rb

@@ -63,6 +63,7 @@ class Room < ApplicationRecord
       bbb.create_meeting(name, bbb_id, create_options)
     rescue BigBlueButton::BigBlueButtonException => exc
       puts "BigBlueButton failed on create: #{exc.key}: #{exc.message}"
+      raise exc
     end
   end