Export Collection from db module.

Currently, Collection is available in the global scope because of
implementation details, but we still need to export Collection from db module
to make the usage of DB API consistent.
Add missing semicolons for plugin JavaScript files.

Using JSHint.
Add native uuid module.

uuid module provides v4() function which returns a type 4 (pseudo randomly
generated) UUID in string.
Make ScriptableDocument support JSON.stringify.