Add Hirb to dev mode gems.
Silence db migrations messages (to console)
require :development mode gems in Rakefile.
Add destroy validations for DhcpProfiles

So that a profile cannot be destroyed if interfaces are still
using it.
Fix quality issue (extra newline)
Fix indentation.
Add a rake task to fire up a development console.

The console has the application loaded (with a db setup). This
allows devs to exercise arbitrary application code without
having to launch a process.