example: implement nearby query

Add "geo" datasource providing access to Google Maps REST API `geocode`.

Add `Location.beforeSave` hook to add a geo code for the address.
example: fix indentation and jshint warnings
example: scaffold rest-api tests

Add `test/end-to-end/example.e2e.js` to scaffold the example app
and run the generated tests against memory datasource.

Add `npm run testdb` script to run the generated tests against all
supported datasources (memory, mongodb, mysql, oracle).
example: customize app URL when running in Cloud9
app: fail in an non-empty directory

loopback-workspace is not able to apply a template to an existing
project, such operation fails with unique-constraint violations.