Add Live view as default home screen. Manage multiple devices

Still work in progress, but live view works now. Log management and
device settings is next.
Add moving average display in live view.

Cannot switch it off for now. Moving average over one minute.
Add Log viewer on separate app screen.

Log download now works, and the "Log Management" screen enables you
to select a device and a log file to display it on the graph. Not
tested on multiple devices.
Restore tooltips on log management screen
Full log management, version 1

App now manages device logs, and is able to manage multiple devices
and multiple logs. For each device, user can graph multiple log
sessions on the same chart, each session appearing in a different
color.

Live view updated, with a graph over the last 2 minutes of readings
and a 1 minute moving average.

Application also now manages the device asset tag and asks the user
to enter it the first time a log is downloaded.
Add more info on log management list of logs