C4.S12 - As a Developer, I can refine search results of synonyms based on demographics and other filtering criteria

Issue #195 
@m0hamed @adamggg @nourhanZ @mostafahassaan 

Files Changed:
Views: search.html.erb
Controllers: SearchController.rb (#search)
model: keyword.rb (retrieve_synonyms method)
Test: keyword_spec.rb
UML: C4.S02.png & C4.S12.png