CMS-800 UI: Facet text search box: Replace trigger with background image

As disquesed with Viktar

Since the facet text box has key event listeners (search is performed as you type) there is no need for a trigger in this text field.

- Remove the trigger
- Keep magnifier glass

See the "search email" text field here:
http://pureinfotech.com/wp-content/uploads/2012/08/Outlook_Inbox_WithChatPanel_Web-850x477.jpg

http://www.pcper.com/files/imagecache/article_max_width/news/2012-08-01/new_outlook_message.jpg
Merge pull request #91 from enonic/CMS-800

CMS-800 UI: Facet text search box: Replace trigger with background image