[configs] Add multimedia keys and a US keyboard layout

To enable Bluetooth headset multimedia keys (play, pause, etc.) the
corresponding keycodes need to be defined. Brought in adenexter's
changes to Jolla keymap config.

To enable Bluetooth keyboards brought in mikkoh's US keymap from Jolla.
Merge pull request #48 from hmallat/keymap-update

[configs] Add multimedia keys and a US keyboard layout