A little refactoring of XML download code
Remove XMLParser.java since it's not used anywhere
Refactor XML parsing away from viewing
Shift storage responsibility from PerkStorage to PerkDataSource. Rename PerkStorage to PerkUpdater because it makes more sense.
Change getCallingActivity() to getContext() because that's all we want from the Activity.
Remove unused imports
Download perk images (XML needs to be modified). Still need to load perk images when viewing.