Fix Gateways Widget Status display

The Gateways Widget Status column did not set the whole color of its box when the status changed (e.g. Online to Offline). Only a bit of the box around the text was having it color changed.
Also the box was missing its right and bottom borders, because it was not declared as class listr.
This set of changes:
1) Makes the Status column class listr, so the bottom and right borders appear nicely.
2) As a result of (1), background-color has been defined in the css of listr, and trying to also specify that with bgcolor in HTML does not work. So use Java Script jQuery to override the default listr color.
3) In get_gatewaystats() also stop trying to specify the bgcolor in a load of HTML. Instead, pass the text and background color through to ajax.js
4) Make ajax.js parse out the text and color and use jQuery to set those.

Seems to work, and I think it is actually better use of CSS.
This finishes fixes for Redmine #4077