Added test xml data files.

re: #11
Removed drink ids from brewer class.

This data is not present in the xml format so has been replaced with a
description which is present.

re: #11
Added test brewers data for xml loading

re: #11
Added tests for generation of brewers from brweries and producers xml.

re: #11
Brewers and producers are now loadable from Xml.

re: #11
Corrected xml creation in test brewer data.

re: #11
Added generation of `Festival` from Xml.

Stripped out most of the Json generation and updated the `Festival`
class to include the additional information from the Xml.

re: #11
Updated `FestivalModel` & tests to use new xml format of data

The model is created with the correct drinks and brewers directly, but
still uses the object based creation and access to allow passing of the
current festival id in the activity's bundle.

re: #11
Added stubs to initialise festival data in main activity.

re: #3
Added object to perform all queries to the web service and simple test.

re: #12
Minor refactor to the `Festival` class

Basically in-lining some expanded variables for conciseness.

re: #12
Added small file to preserve the assets directory.
Initialised festival model in main activity, if not already done.

Added implicit conversion for string to Xml in `XmlHelpers`

re: #2