(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/Search.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 / Search</title>
+    <desc>Created with Sketch.</desc>
+    <g id="Icons-/-UI-/-Search" stroke="none" stroke-width="1" fill="none" fill-rule="evenodd">
+        <path d="M11.4362127,10.7291059 L14.8535534,14.1464466 C15.0488155,14.3417088 15.0488155,14.6582912 14.8535534,14.8535534 C14.6582912,15.0488155 14.3417088,15.0488155 14.1464466,14.8535534 L10.7291059,11.4362127 C9.59233848,12.4110487 8.11494771,13 6.5,13 C2.91014913,13 0,10.0898509 0,6.5 C0,2.91014913 2.91014913,0 6.5,0 C10.0898509,0 13,2.91014913 13,6.5 C13,8.11494771 12.4110487,9.59233848 11.4362127,10.7291059 Z M10.4095747,10.3684921 C11.3928325,9.3748578 12,8.00833468 12,6.5 C12,3.46243388 9.53756612,1 6.5,1 C3.46243388,1 1,3.46243388 1,6.5 C1,9.53756612 3.46243388,12 6.5,12 C8.00833468,12 9.3748578,11.3928325 10.3684921,10.4095747 C10.3749001,10.4023879 10.3815516,10.3953416 10.3884466,10.3884466 C10.3953416,10.3815516 10.4023879,10.3749001 10.4095747,10.3684921 Z" id="Combined-Shape" fill="#000000" fill-rule="nonzero"></path>
+    </g>
+</svg>