Add "connecting" and "disconnecting" states to HID Device.

Currently the upper java layers have full support for all four
connection states, yet the lower stack only reports about
"connected" and "disconnected".
This patch adds sending "connecting" and "disconnecting" messages
when bta_hd_connect_act and bta_hd_disconnect_act finish
successfully.

Test: build, run, logcat
Change-Id: I00f9f414daa3854198ff9eee19e9c98a2e18f603