Refactor: move model and CMR stubs here

[CeylonMigrationBot]

[@FroMage] To be able to run Ceylon code at runtime without JBoss Modules nor CMR support we need to:

• move the model from the typechecker to here
• move the model loader from the jvm compiler to here
• move some CMR interfaces to here (those used by the language module and the two above components)

Then we can make it so the language module can run without typechecker/compiler/cmr/runtime when using a flat classpath.

[Migrated from ceylon/ceylon-common#41]

[CeylonMigrationBot]

[@quintesse] It's not for 1.2, I know, but I just wanted to know if the status of this issue has changed now that we have ceylon-model?