[SDL 0148] Template Improvements: Additional SubMenus

[theresalech]

Proposal: Template Improvements: Additional SubMenus

Currently, SDL is by far the most restrictive among its competitors for drilling down into menus. It only allows the top menu and one submenu (additional submenus can be "faked" using Choice Sets). CarPlay, for example, allows at least 3 levels of drilling, this was the most I could find in the apps I use (in addition to tabs at the top, which is a kind-of 4th level). CarPlay allows as much drilling as desired by the user in the car, but prevents scrolling while moving. For future updates, we should allow further menu depth. For driver distraction reasons, a later proposal will allow restriction of menu depth while driving to replicate current restrictions if desired.

Review: smartdevicelink/sdl_evolution#423

Steering Committee Decision:

The Steering Committee has voted to accept this proposal with the following revisions: update proposal to only include details regarding "Allowing Submenu's with parentID's that refer another Submenu." A separate proposal will be entered to discuss "Allowing Core to define driver distraction parameters for HMI."

When discussing submenus, a few additional points were made:

Right now, this is only considered for submenus, but driver distraction guidelines could be extended to include choice sets for interactions as well (including list length)
Proposal outlines the same behavior as is currently in place for submenus, but extends to allow a submenu to have a submenu

The proposal .md was updated on March 22, 2018 to include the agreed upon revisions.