Try to make the power monitor more robust

Try to reconnect to upowerd if using our current connection to it fails.
Add template support to the network widget.

Allow users to choose how to display network information in a
backwards-compatible way.
[NetMonitor] Commentary and warning cleanup
Start a changelog for the next release
[CommandRunner] Add a new widget

This widget periodically runs commands and displays the output in a text widget.
[CPUInfo] Add a function to get CPU temperature
Add the command runner widget to the changelog
Reduce wakeups by tweaking RTS options

Found with the prompting and help of Joachim Breitner
[Command Runner]  Cleanups

Use a function from System.Process instead of re-implementing it.  The
only difference between this and the original is that stderr from the
subprocess is buffered.  This probably isn't a big deal since most uses
of taffybar would hide stderr anyway.