(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/ui/AppHeader.ts

@@ -0,0 +1,60 @@
+import {urlState} from 'app/client/models/gristUrlState';
+import {getTheme, ProductFlavor} from 'app/client/ui/CustomThemes';
+import {cssLeftPane} from 'app/client/ui/PagePanels';
+import {colors, testId, vars} from 'app/client/ui2018/cssVars';
+import * as version from 'app/common/version';
+import {BindableValue, dom, styled} from "grainjs";
+
+export function appHeader(orgName: BindableValue<string>, productFlavor: ProductFlavor) {
+  const theme = getTheme(productFlavor);
+  return cssAppHeader(
+    urlState().setLinkUrl({}),
+    cssAppHeader.cls('-widelogo', theme.wideLogo || false),
+    // Show version when hovering over the application icon.
+    cssAppLogo({title: `Ver ${version.version} (${version.gitcommit})`}),
+    cssOrgName(dom.text(orgName)),
+    testId('dm-org'),
+  );
+}
+
+const cssAppHeader = styled('a', `
+  display: flex;
+  width: 100%;
+  height: 100%;
+  align-items: center;
+  &, &:hover, &:focus {
+    text-decoration: none;
+    outline: none;
+    color: ${colors.dark};
+  }
+`);
+
+const cssAppLogo = styled('div', `
+  flex: none;
+  height: 48px;
+  width: 48px;
+  background-image: var(--icon-GristLogo);
+  background-size: 22px 22px;
+  background-repeat: no-repeat;
+  background-position: center;
+  background-color: ${vars.logoBg};
+  .${cssAppHeader.className}-widelogo & {
+    width: 100%;
+    background-size: contain;
+    background-origin: content-box;
+    padding: 8px;
+  }
+  .${cssLeftPane.className}-open .${cssAppHeader.className}-widelogo & {
+    background-image: var(--icon-GristWideLogo, var(--icon-GristLogo));
+  }
+`);
+
+const cssOrgName = styled('div', `
+  padding: 0px 16px;
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  .${cssAppHeader.className}-widelogo & {
+    display: none;
+  }
+`);