Added year and week to XTimeOverview.

Makes it possible to identify the time sheets in the database.
Implemented XTimeProvider for time registration data.

 The structure is inspired by the Google IO 2014 app. The SQlite database contains three tables: time_sheets, time_sheet_rows, time_entries. There is a separate XTimeContract class that contains the database schema contracts, with column names and URIs.
Updated sync adapter to use the XTimeProvider for storage.
Load data from content provider instead of HTTP.