(core) Redirect less often in welcomeNewUser

Summary:
Instead of always redirecting new users to the home page or the (teams) welcome page,
only redirect when the user signed in for the first time on a personal site, has access to
other sites, and isn't already being redirected to a specific page on their personal site.

Also tweaks how invalid Choice column values are displayed to match Choice List
columns, and fixes a small CSS issue with select by in the page widget picker when
there are options with long labels.

Test Plan: Browser tests.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D3461

app/common/gristTypes.ts

@@ -200,19 +200,7 @@ const rightType: {[key in GristType]: (value: CellValue) => boolean} = {
   ManualSortPos:  isNumber,
   Ref:            isNumber,
   RefList:        isListOrNull,
-  Choice:         (v: CellValue, options?: any) => {
-    // TODO widgets options should not be used outside of the client. They are an instance of
-    // modelUtil.jsonObservable, passed in by FieldBuilder.
-    if (v === '') {
-      // Accept empty-string values as valid
-      return true;
-    } else if (options) {
-      const choices = options().choices;
-      return Array.isArray(choices) && choices.includes(v);
-    } else {
-      return false;
-    }
-  },
+  Choice:         isString,
   ChoiceList:     isListOrNull,
 };