(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/lib/browserGlobals.js

@@ -0,0 +1,54 @@
+/**
+ * Module that allows client-side code to use browser globals (such as `document` or `Node`) in a
+ * way that allows those globals to be replaced by mocks in browser-less tests.
+ *
+ * E.g. test/client/clientUtil.js can replace globals with those provided by jsdom.
+ */
+
+
+var allGlobals = [];
+
+/* global window */
+var globalVars = (typeof window !== 'undefined' ? window : {});
+
+/**
+ * Usage: to get access to global variables `foo` and `bar`, call:
+ *    var G = require('browserGlobals').get('foo', 'bar');
+ * and use G.foo and G.bar.
+ *
+ * This modules stores a reference to G, so that setGlobals() call can replace the values to which
+ * G.foo and G.bar refer.
+ */
+function get(varArgNames) {
+  var obj = {
+    neededNames: Array.prototype.slice.call(arguments),
+    globals: {}
+  };
+  updateGlobals(obj);
+  allGlobals.push(obj);
+  return obj.globals;
+}
+exports.get = get;
+
+/**
+ * Internal helper which updates properties of all globals objects created with get().
+ */
+function updateGlobals(obj) {
+  obj.neededNames.forEach(function(key) {
+    obj.globals[key] = globalVars[key];
+  });
+}
+
+/**
+ * Replace globals with those from the given object. The previous mapping of global values is
+ * returned, so that it can be restored later.
+ */
+function setGlobals(globals) {
+  var oldVars = globalVars;
+  globalVars = globals;
+  allGlobals.forEach(function(obj) {
+    updateGlobals(obj);
+  });
+  return oldVars;
+}
+exports.setGlobals = setGlobals;