ShortcutManager: API rename

The words "title" and "text" implies that "text" is a secondary label
that's shown with the title, but it turned out the launcher would show
only one of those depending on how much space it has.

So now we change them to "shortLabel" and "longLabel"

Note we're only changing the API surface -- in order to mimimize
the impact to the code, internally we'll keep using the old names.

- Also remove "shortcutRank" while I'm here -- it should be implied
from the order of the XML elements.

Bug 29057378

Change-Id: I3203f63b0318c7462c1c61fef43cf9755fa8c008