Introduce mandatory `last_updated_at` field

Also rename last_modified to same naming convention
Use different class variable name for class-based (as opposed to module-based) bots
Added executables as aliases to common rake tasks
Require last_updated_at as a method.

Also improve runtime checks that record conforms to interface.
Merge pull request #14 from openc/misc-fixes-seb

Fixes to make new bots work without errors