Home screen shortcuts.

There's one issue that needs to be ironed out. Once the user creates a shortcut
to a HistoryItem and later modifies the HistoryItem via the application,
the shortcut is not updated.

Initially this wasn't an issue because each Shortcut was associated with
a HistoryItem id so the values were read directly from the database
every time the shortcut was triggered. However if the user deletes the
said HistoryItem this would leave the shortcut in an invalid state. 

To avoid this in my last commit I resorted to copying over the needed
details of the selected HistoryItem to the Shared Preferences of the
shortcut and hence if the original HistoryItem is modified the shorcut
is not changed.