(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/UI/CenterAlign.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 / UI / CenterAlign</title>
+    <desc>Created with Sketch.</desc>
+    <g id="Icons-/-UI-/-CenterAlign" stroke="none" stroke-width="1" fill="none" fill-rule="evenodd">
+        <path d="M5.5,8.5 C5.22385763,8.5 5,8.27614237 5,8 C5,7.72385763 5.22385763,7.5 5.5,7.5 L10.5,7.5 C10.7761424,7.5 11,7.72385763 11,8 C11,8.27614237 10.7761424,8.5 10.5,8.5 L5.5,8.5 Z M2.5,4 C2.22385763,4 2,3.77614237 2,3.5 C2,3.22385763 2.22385763,3 2.5,3 L13.5,3 C13.7761424,3 14,3.22385763 14,3.5 C14,3.77614237 13.7761424,4 13.5,4 L2.5,4 Z M4,13 C3.72385763,13 3.5,12.7761424 3.5,12.5 C3.5,12.2238576 3.72385763,12 4,12 L12,12 C12.2761424,12 12.5,12.2238576 12.5,12.5 C12.5,12.7761424 12.2761424,13 12,13 L4,13 Z" id="Combined-Shape" fill="#000000" fill-rule="nonzero"></path>
+    </g>
+</svg>