[SDL 0259] Disabled Softbuttons

[theresalech]

Proposal: Disabled Softbuttons

This feature would allow apps to send custom softbuttons to display on screen but they would appear disabled. This also allows an app to subscribe to and disable SDL predefined buttons.

Review: https://github.com/smartdevicelink/sdl_evolution/issues/859

Steering Committee Decision:

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

• Use disabledSupported in place of disabledButtonPossible param within ButtonCapabilites and make parameter mandatory="false".
• Use disabledSupported in place of disabledAvailable param within SoftButtonCapabilites param.
• Change param isDisabled to the following:

public boolean isDisabled() { ... }
public void setDisabled(bool disabled) { ... }

@property (assign, nonatomic, getter=isDisabled) BOOL disabled;

• Specify in the proposal that once SDL-0250 is implemented, if there is a case where both the HMI and app attempt to disable a button, the HMI disabling will override the app's.

The proposal .md file was updated to reflect these revisions on 1/29/2020.