Allow user to search for agencies

This allows the user to do either a quick search (just entering a keyword and searching through the agency names, zipcodes, and city) OR doing an advanced search with multiple fields.  Any of the fields can be used but they don't have to be. Additional fields will be added later. 
oh got it. i thought i remembered that we often used form_tag when there is nothing being added to the model (this is a search, so nothing real being created).