Move isBrowser and isServer from lib/loopback to a new file lib/runtime.
Move all Model and DataSource related methods like `createModel` and
`createDataSource` to lib/registry.
Remove the circular dependency between lib/application and lib/loopback,
by loading lib/registry and/or lib/runtime instead of lib/loopback
where appropriate
This commit is only moving the code around, the functionality should
not be changed at all.
7d674779e1