(core) move client code to core

Summary:
This moves all client code to core, and makes minimal fix-ups to
get grist and grist-core to compile correctly.  The client works
in core, but I'm leaving clean-up around the build and bundles to
follow-up.

Test Plan: existing tests pass; server-dev bundle looks sane

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2627

app/client/exposeModulesForTests.js

@@ -0,0 +1,13 @@
+/* global window */
+
+// These modules are exposed for the sake of browser tests.
+Object.assign(window.exposedModules, {
+  dom: require('./lib/dom'),
+  grainjs: require('grainjs'),
+  ko: require('knockout'),
+  moment: require('moment-timezone'),
+  Comm: require('./components/Comm'),
+  ProfileForm: require('./components/ProfileForm'),
+  _loadScript: require('./lib/loadScript'),
+  ConnectState: require('./models/ConnectState'),
+});