Shopping List Regex, DatabaseModelTest comments, new test file

Replaced the check for "" input on shopping list with a regex that
checks for any number of space characters

Added some comments to the DatabaseModelTest class

Created a DatabaseModelFailTest class to test instances when the
database doesn't exist/sqlite exceptions

Edited the Android XML so that only Tutorial Activity has the Main and
Launcher attributes.
Merge branch 'master' of github.com:jfmyers9/ThePantry