Menu Widget - Add title and separator options

[AdRiley]

The title and separator bar need to be configurable from the library code
They should not be selectable or highlight

[farmaazon]

Refinement notes:

• Both title and separator could be same element - just separator without title is a line
• In the protocol, we should consider just grouping elements instead of defining a special "separator" element (similarly to nested menus).
• The exact behavior of filtering is not specified - may be same as in submenu case, for simplicity. There was an idea of configuration having options for filtering - not in this task.