Can't configure baseUrl for require.js

Currently there is no way to provide an alternative ```baseUrl``` for the [config](https://github.com/cwrc/CWRC-Writer/blob/53d9227116e2428aadedc502be5051def17d8cdb/src/js/config.js#L2) for require.js

If we don't specify a default and instead just use the default behaviour (when using data-main, as the entry point) as noted here:
http://requirejs.org/docs/api.html#config-baseUrl

> If no baseUrl is explicitly set in the configuration, the default value will be the location of the HTML page that loads require.js. If a data-main attribute is used, that path will become the baseUrl.

Both Islandora and CWRC should be able to provide their own custom ```baseUrl```. This will work for the existing CWRC-Writer without any changes to ```editor_dev.htm```.