VEX-5682: iOS Swift Conversion

[nickfujita]

Converts iOS implementation from objc to swift

Jira: VEX-5682
https://jira.tenkasu.net/browse/VEX-5682

Velocity PR: https://github.com/crunchyroll/velocity/pull/1966

[nickfujita]

@cristi-lupu There is probably more cleanup and improvement that can be done, but going to cap off the work here in order to move forward on the project. All previous functionality should be working the same.

Would you mind having a look over the Swift code, and provide any feedback on improvements that can be made to the syntax or patterns used?

[cristi-lupu]

Is there any reason you want to keep the initial dictionary object? Applicable for other models as well.

[nickfujita]

since there is logic that sends back the input dictionary back to the client, instead of converting to DRMParams, then converting back to NSDictionary, this keeps a reference to the original to simply send back

[nickfujita]

@cristi-lupu thanks for reviewing the swift code! updated.