Feature/soft button manager queues

[crokita]

Fixes #454

Risk

This PR makes no API changes.

Testing Plan

• I have verified that I have not introduced new warnings in this PR (or explain why below)
• I have verified that this PR passes lint validation
• I have run the unit tests with this PR
• I have tested this PR against Core and verified behavior (if applicable, if not applicable, explain why below).

Unit Tests

Matches the Java library tests for this class in its state on the develop branch.

Summary

Adds operational classes and refactors the SoftButtonManager to use asynchronous task queues.

Additional Changes

• Added extra validation methods for tests
• SoftButtonState now has a default system action
• SoftButtonObject will report if attempting to transition when there's only one state
• SdlArtwork will not perform an action if the value passed to setType is undefined (for SoftButtonObject cloning purposes)

[renonick87]

See minor feedback.