We are only able to store static content at the dashboard (app) level.
This forces us to store all of our statics under the dashboard's static folder.
This patch introduces a panel static finder. Django's static finder will now
find files inside the panel's static folder as well. This is more inline with what
we have today for python plugins.
Change-Id: I2bb3f78abf8854dbad8f1697d942f94d36014d41
Closes-Bug: #1544295