Keyboard shortcuts: A11Y fixes

* Letters are no more announced as capitals
* Focus now moves into the function key buttons (images)
* The keyboard shortcuts are not being verbalized individually
but instead the whole group is now verbalized in one go.

Bug: 29267887
Bug: 29259734
Bug: 29260915
Change-Id: Ie2cf519338cbb7d07c2d52b419dcf6b5a9e14147