Add homepage redirect configuration

-COLAB_HOME_URL in settings.py sets the homepage redirect, empty to
ignore configuration

Signed-off-by: Gustavo Jaruga Cruz <darksshades@gmail.com>
Add default home to dashboard

-Sets colab old home as Dashboard
-Default setting of home to dashboard

Signed-off-by: Gustavo Jaruga <darksshades@gmail.com>
Moved COLAB_HOME_URL higher in the file