Added legacy transformation, currently no tests for new JWT structure

[SecondeJK]

T1 tokens are being marked as legacy to increase security. Instead, SHA256 encoded JWTs will be used by default.

Description

generateToken() now takes a default parameter that is set to true unless specifically set by the user. To use the old T1 tokens for backwards compatibility, set the parameters like so:

$client = new OpenTok\OpenTok();
$token = $client->generateToken(API_KEY, API_SECRET, [], true);

Motivation and Context

Increased security

How Has This Been Tested?

Tests coming for the new tokens when exact setup of claims has been identified.

Example Output or Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.