add conditional module.postinstall event 

add conditional module.postinstall event that when fired can be used for route loading. modify listener to compensate. fixes #1959 

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #1959
| Refs tickets  | -
| License       | MIT
| Doc PR        | -

ping @cmfcmf @Guite