Fix mysql and default to sqlite

Two things I did here:

1) I put back the defaults you set up for the content types, but made them work okay for an initial MySQL migration

2) I then removed PostgreSQL (and MySQL) from the default configuration, and instead have the project defaulting to sqlite. I figured if people install this, make it easy for them, and let them change to whatever they want - if they want. But don't add complexity at the start.

Also added a line to the instructions to precompile assets, and called out RAILS_ENV=production on the setup stuff for the DB, because that seems to be what the instructions are guiding you through. 

(I plan on simplifying setup more, BTW... Your default statuses and stuff currently in seeds - and also called out in instructions - I want to just add these default statuses and stuff in as a migration. People can change them later)