All 'sent' rows including the row header have the alt color, and
the 'recv' rows including the row header has the base color. This
change should make it easier to quickly distinguish sent/recv rows
* All 3 icons are combined into a single row instead of 3 separate rows
* Tooltip to clarify meaning of icons
* Qt Model-View displays icon left-aligned, so use a custom delegate to
center-align it
* Add a icon for "Transmit On"
* Edit icons for "Start/Stop Capture"
bps stats are derived from the Bps stats and represent line rate taking
into account the per packet overhead on the line with the following
assumptions -
* Link type is Ethernet
* Bps (and total Bytes) stats don't include the 4-byte FCS
Fixes#241