Add file "alt icon" that is used when app can be used with active tab.

* browserAction icon uses alt icon currently for amazon and ebay (sites in the scrapeDefinitions)
* content_script calls refreshIcon in backgroundScript when page is loaded
* Add file "alt icon" that is used when app can be used with active tab.
* browserAction icon uses alt icon currently for amazon and ebay (sites in the scrapeDefinitions) - content_script calls refreshIcon in backgroundScript when page is loaded
* Improve style for pop-up
* add $ sign to popup