Temporarily disable SMTP email backend on staging/production
Temporarily disable SMTP email backend on staging/production

This fixes a bug where user registration throws an Internal Server
Error on staging. The fix is to temporarily disable the SMTP email
backend until we have configured it properly on AWS.

Test by successfully creating a user on staging and logging in as that
user.

Connects #287

azavea/raster-foundry,azavea/raster-foundry,aaronxsu/raster-foundry,azavea/raster-foundry,kdeloach/raster-foundry,raster-foundry/raster-foundry,kdeloach/raster-foundry,azavea/raster-foundry,kdeloach/raster-foundry,aaronxsu/raster-foundry,kdeloach/raster-foundry,aaronxsu/raster-foundry,azavea/raster-foundry,raster-foundry/raster-foundry,raster-foundry/raster-foundry,aaronxsu/raster-foundry,kdeloach/raster-foundry