CMSensor -- start recording should not be on main thread

[gcmcnutt]

this causes a blockage, for example, when the authorization pop up shows up on phone

[gcmcnutt]

This also fixed the problem with the record button label -- now it updates during the initial flow from cold install:

• on first launch the label is 'not yet auth', when the user hits this, the auth popup will show on the phone, if the user says yes, then the button label will change -- also the last start flow is better being async going through a 'starting...' phase followed by a value.

note: i don't yet alter the value of the last start -- thinking if this needs something -- similarly an alert should show up on watch when auth is set to false -- only after the first attempt (stating -- you may need to set privacy->motion&fitness->sensor2 to on to capture accelerometer events