Partial rewrite of traffic indicator

[log]

- lower system impact: nothing runs when screen is off (previous version ran continuously unless the network speed indicator was disabled
- show summary of traffic when traffic stops (number of bytes in the current "burst")
- better formatting of the indicator

Remaining to improve:

- stop the indicator when the status bar is hidden (can't figure out how to get notifications when it does get hidden)

Change-Id: Iae248454a9f66979eb6c8148ac91faf820764831

Traffic meter: show summary of traffic in brackets

Change-Id: I00b056bc0076fdc9e3d573dfe4b0fb7c7aa11e0a

Update color

Change-Id: I25def4f1aee41f8dc216bbba10832b618d5f3a2a