activity: basic query support

only supports queries of fields actually in Activity. The web UI only
directly queries two of these, ID and Time (mistakenly referneced as date in
the web ui previously). Later commits will come up with creative ways of
dealing with all the other query types.

ts/modules/activity.ts

@@ -74,9 +74,9 @@ const queries = (): { [field: string]: QueryType } => { return {
         string: true,
         date: false
     },
-    "date": {
+    "time": {
         name: window.lang.strings("date"),
-        getter: "date",
+        getter: "time",
         bool: false,
         string: false,
         date: true