Edits to strings to meet UI text standards.

* Use contractions.
* Use \u2026 instead of ... for ellipsis.
* Use straight quotes (for now that's the standard).
* Made the permission descriptions consistent.
* Use sentence case everywhere except for proper nouns.
* Notification messages need ending punctuation.
* Use "touch" instead of "tap".
* Use "choose" instead of "select", except when selecting text.
* Use "sign into" instead of "sign in to".
* Use "Do you want..." instead of "Would you like..."
* Autofill has only initial cap.

Also, please check this change I made to make the string more user-friendly:
  <string name="gadget_host_error_inflating">Error inflating widget</string>
+ <string name="gadget_host_error_inflating">Couldn\'t add widget.</string>

Bug: 5163232
Bug: 5162328
Bug: 5162667
Change-Id: I6667171f3e3d089319c5acd59088c20ff69a845e

A few more edits caught by self-review.

Change-Id: I6667171f3e3d089319c5acd59088c20ff69a845e

Two edits flagged by reviewer.

Change-Id: I6667171f3e3d089319c5acd59088c20ff69a845e