Recognize 'group' as a valid parameter name in search queries

The backend already supports searches for 'group:hashid' but
this was not supported on the stream because 'group'
was not recognized as a valid parameter so it was passed
to the backend in the 'any' field.

h/static/scripts/search-filter.coffee

@@ -12,7 +12,8 @@ module.exports = class SearchFilter
       # The whole term is data
       return [null, term]
 
-    if filter in ['quote', 'result', 'since', 'tag', 'text', 'uri', 'user']
+    if filter in ['group', 'quote', 'result', 'since',
+                  'tag', 'text', 'uri', 'user']
       data = term[filter.length+1..]
       return [filter, data]
     else

h/static/scripts/test/search-filter-test.coffee

@@ -26,12 +26,13 @@ describe 'searchFilter', ->
       assert.equal(result.any[0], query)
 
     it 'uses the filters as keys in the result object', ->
-      query = 'user:john text:foo quote:bar other'
+      query = 'user:john text:foo quote:bar group:agroup other'
       result = searchFilter.toObject(query)
       assert.equal(result.any[0], 'other')
       assert.equal(result.user[0], 'john')
       assert.equal(result.text[0], 'foo')
       assert.equal(result.quote[0], 'bar')
+      assert.equal(result.group[0], 'agroup')
 
     it 'collects the same filters into a list', ->
       query = 'user:john text:foo quote:bar other user:doe text:fuu text:fii'