Set licence_key in TinyMCE config

[aaronskiba]

Fixes #791

Changes proposed in this PR:

• From https://www.tiny.cloud/docs/tinymce/latest/license-key/?utm_campaign=console_license_key_message&utm_source=tinymce&utm_medium=referral
• "TinyMCE 7 is licensed under the GNU General Public License Version 2 or later. A new configuration option called 'license_key' requires developers to make a conscious decision to use TinyMCE with the GPLv2+ license or with a commercial license. If you are using TinyMCE in a self-hosted environment, a console log warning message will display if the license key config option is missing or invalid. This message aims to ensure compliance with licensing requirements and provide transparency during the evaluation period."