(core) Adds current page name to the bottom bar [narrow screen]

Test Plan: Tested Manually, behave well also for long page name.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2702

app/client/ui/BottomBar.ts

@@ -0,0 +1,16 @@
+import {DocPageModel} from 'app/client/models/DocPageModel';
+import {dom, MultiHolder, styled} from 'grainjs';
+
+
+export function createBottomBarDoc(owner: MultiHolder, pageModel: DocPageModel) {
+  return dom.maybe(pageModel.gristDoc, (gristDoc) => (
+    cssPageName(dom.text(gristDoc.currentPageName))
+  ));
+}
+
+const cssPageName = styled('div', `
+  margin: 0 10px;
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+`);