(core) add docs.options column to home db to store doc description, icon, openMode

Summary:
Bundles some new document options into a JSON column.
The icon option is treated somewhat gingerly.  It is intended, at
least initially, to store an image thumbnail for a document as a
url to hand-prepared assets (for examples and templates), so it is
locked down to a particular url prefix to avoid opening the door to
mischief.

Test Plan: added test

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D2916

app/server/lib/requestUtils.ts

@@ -193,6 +193,8 @@ export function pruneAPIResult<T>(data: T): T {
       // Do not include removedAt field if it is not set.  It is not relevant to regular
       // situations where the user is working with non-deleted resources.
       if (key === 'removedAt' && value === null) { return undefined; }
+      // Don't bother sending option fields if there are no options set.
+      if (key === 'options' && value === null) { return undefined; }
       return INTERNAL_FIELDS.has(key) ? undefined : value;
     });
   return JSON.parse(output);