Android - Implement support for space separated scopes

[mribbons]

I had an issue with http://github.com/identityServer/IdentityServer3 where it expects a space separated list of scopes, while react-native-oauth supports a comma separated list.

In the previous code, spaces are removed before the string is split by comma.

To use the option:

    manager.addProvider({
        'our_provider': {
            auth_version: '2.0',
            authorize_url: 'http://example.com/authorize',
            access_token_url: 'http://example.com/token',
            access_token_verb: 'post',
            api_url: 'http://example.com/api',
            callback_url: ({app_name}) => `${app_name}://oauth`
        }
    });

    manager.configure({
      our_provider: {
        client_id: 'sample',
        client_secret: 'secret',
        consumer_key: 'must_be_provided_for_custom_provider',
        api_key: 'must_be_provided_for_custom_provider',
        consumer_secret: 'must_be_provided_for_custom_provider',
        rawScopes: 'true'
      }
    });

    manager.authorize('our_provider', {scopes: 'openid profile api1'});

This resolves the issue.

Note that I have not tested with ios.

Note that this PR is similar to a0dd695, except that it is a non breaking change.