[SDL 0243] Manager Update for DisplayCapability

[theresalech]

Proposal: Manager Update for DisplayCapability

This proposal adds display capabilities redesign described in SDL 0216 Widget Support (see issue #664) to SystemCapabilityManager.

Review: smartdevicelink/sdl_evolution#797

Steering Committee Decision:

The Steering Committee voted to accept this proposal with the following revisions:

• In addition to- (nullable SDLWindowCapability *)windowWithID:(NSNumber<SDLInt> *)windowID; , include - (nullable SDLWindowCapability *)mainDisplayMainWindowCapabilities; with property defaultMainWindowCapability
• Change “In order to avoid clashes with the mobile API the enum should not be extended any further without adding the enum values to the mobile API.” to “In order to avoid clashes with the mobile API the enum should only be extended with extreme caution when absolutely necessary or by adding the enum values to the RPC Spec.”

The proposal .md file was updated to reflect these revisions on 8/22/19.