update gems

so that we have the latest patches and security updates
drop name and desc attributes from gem_checker_result ...

 because we don't use them
add schema.rb with the previous migrations applied
add validation to gem_checker_results
validate gem_info attributes

add some validation to the gem_info model
validate has_changed attributes

also refactor some common code and fix the db:populate:dev task
remove duplicate license field in gem checker
add validation to is_latest_version model and fix db:populate:dev
remove license attribute from database that is not being used
add validation to is_native
add validation to is_rubygems model
add validation to security_alert model