Make the template lookup for installers more flexible

Though we don't use it yet, it's now possible to have both templates stored
in the FS, and templates that are stored in the DB as text.
* db/migrate/002_create_base_schema.rb: move validation regexps to constants

We will want to use these for other validations, too
Allow storing installers in the DB in addition to the FS
* lib/razor/installer.rb (find): look for installers in FS and in DB
Add a 'create_installer' command
Documentation for the create_installer command