Addressable scene loading

[kroecks]

Addressable scene loader changes

[unity-cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
6 out of 7 committers have signed the CLA.

:white_check_mark: jonathanhertz
:white_check_mark: DSchroer
:white_check_mark: EmandM
:white_check_mark: simon-lemay-unity
:white_check_mark: NoelStephensUnity
:white_check_mark: michalChrobot
:x: kroecks
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[kroecks]

Changes for loading scenes through addressables. This review is not meant to be merged The addressable asset name must match the scene name to load in order to function.

[EmandM]

Hi! Thanks for your contribution. Unfortunately this pull request is far too large to consider merging. If the changes made in this PR are still relevant, please open a new PR with only the relevant files and areas changed, and no changes elsewhere. Thank you!