BeerXML Support

[DougEdey]

This is the first set of commits, I'll be doing some tidying up tonight to sort some things out, but I figured I'd push this so you can take a look first.

• Add a Quantity class which supports conversion between different weight types
• Allow Weight to use a string constructor which creates a Quantity class then converts this back to ounces as the Weight default.
• Add a basic BeerXML parser that uses XPath lookup (there's no DTD for BeerXML that I can find)
  ** Returns an array of recipes
• Add an "Open" option to the RecipeListFragment that will allow XML files to be selected
  • This will determine that the file is a BeerXML file then opens the BeerXML parser.
  • This allows us to support more filetypes in the future.
• Add a ParseXML class that has a helper that identifies the recipe type (either via File path or InputStream)
• If a list of recipes comes back, add them all to the Datastore.
• if one recipe comes back, show it, otherwise just refresh the list.

[edrews]

Can we make 'quantity' a method variable? Otherwise I think GSON will try to serialize the 'quantity' member variable to storage.

[DougEdey]

I made it into a member variable since it is a more convertable friendly class. I would prefer to use it instead of Weight (or bring the same functionality to Weight) that allows conversions between units (i.e. allows you to convert a value from Ounces to grams or to pounds or whatever you want.

[edrews]

Hey, just a couple of comments above. The BeerXML branch looks awesome. I'm ready to merge just this in if that's cool.

[DougEdey]

Updated as per the comments. You can merge this whenever you want, I'll add BeerXML export later.

[edrews]

I do like the Quanity class better than the Weight class. I have no problem replacing it provided it doesn't break support for already-created recipes.