Installation: Add warning to initial setup script

[dsajdak]

As part of the installation, we run coldfront initial_setup which sets up defaults like attribute types and other example info. We do not recommend using this for existing installations and want any changes to ColdFront code to be added to the migrations functionality. This will allow existing users who upgrade ColdFront to get the necessary changes but not affect their existing data. We do want to add a warning message to this initial_setup just in case someone runs this without realizing it will delete existing data. Some like:

"WARNING: Running this command initializes the ColdFront database. This should only be run one time. Running this will delete anything currently in the ColdFront database. Do you want to proceed? Yes/No"