We have a few apps that were given more explicit, namespaced app labels

in Djblets 2.0.dev. Since we're supporting Django 1.11 and Django

Evolution 2.0 now, we need to be able to clearly distinguish between app

labels and to make sure that the evolution project signature is using

the right app labels for the right apps.
To help this along, this change adds evolutions that define the app

label for some of our apps, taking the guesswork out of it and ensuring

that the project signature is evolved correctly.

Unit tests passed.
Tested evolving the database on Django 1.6 and 1.11 with Review Board 4.0.