base.html:
- don't show drop down for user's projects if the user doesn't belong to any projects.
forms.py:
- override PanelForm __init__ method to limit available sites to those belonging to the project

urls.py:
- created a generic TemplateView for redirecting warning messages...this avoids putting template code everywhere checking for messages

views.py:
- added checks for whether a project has any sites when a user tries to create a new panel