Replace Filter class with expression structure

This is in order to be able to support UPPER() and LOWER() functions in
queries which are needed for case-insensitive search.

client/app.js

@@ -11,7 +11,6 @@ import * as devicePage from "./device-page";
 import * as errorPage from "./error-page";
 import * as faultsPage from "./faults-page";
 import Authorizer from "../common/authorizer";
-import * as funcCache from "../common/func-cache";
 
 window.authorizer = new Authorizer(window.permissionSets);
 
@@ -69,8 +68,6 @@ function pagify(pageName, page) {
   return component;
 }
 
-setInterval(funcCache.purge, 120000);
-
 m.route(document.body, "/overview", {
   "/login": pagify("login", loginPage),
   "/overview": pagify("overview", overviewPage),