[SDL 0321] Add Current Template Name to Window Capabilities

[jordynmackool]

Proposal: Add Current Template Name to Window Capabilities

This proposal adds a new optional parameter to the WindowCapability struct containing the current template name, and a new app library ScreenManager parameter to assist app developers in tracking the current template.

Review: smartdevicelink/sdl_evolution#1087

Steering Committee Decision:

The Steering Committee voted to accept this proposal with revisions. The author will update the proposal to include the revisions described in this comment.

The proposal .md file was updated to reflect these revisions on 12/9/2020.