[2.2][Propel1] re-factor Propel1 ModelChoiceList

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | fixes propelorm/Propel#789
| License       | MIT

replaces #9458