(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

static/ui-icons/Fields/FieldAny.svg

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg width="16px" height="16px" viewBox="0 0 16 16" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+    <!-- Generator: Sketch 52.5 (67469) - http://www.bohemiancoding.com/sketch -->
+    <title>Icons / Fields / FieldAny</title>
+    <desc>Created with Sketch.</desc>
+    <g id="Icons-/-Fields-/-FieldAny" stroke="none" stroke-width="1" fill="none" fill-rule="evenodd">
+        <path d="M9.14644661,6.14644661 C9.34170876,5.95118446 9.65829124,5.95118446 9.85355339,6.14644661 C10.0488155,6.34170876 10.0488155,6.65829124 9.85355339,6.85355339 L8.08668514,8.62042164 L9.47775309,12.0980915 L12.66395,3.33604999 L3.90190848,6.52224691 L7.37957836,7.91331486 L9.14644661,6.14644661 Z M7.11534537,8.88465463 L2.31430466,6.96423835 C1.88803098,6.79372887 1.89765916,6.18700122 2.32912847,6.03010329 L13.3291285,2.03010329 C13.7281416,1.88500761 14.1149924,2.27185841 13.9698967,2.67087153 L9.96989671,13.6708715 C9.81299878,14.1023408 9.20627113,14.111969 9.03576165,13.6856953 L7.11534537,8.88465463 Z" id="Path" fill="#000000" fill-rule="nonzero"></path>
+    </g>
+</svg>