Backport template plugin from TinyMCE 6

[petschki]

No description provided.

[1letter]

i tested this here in my local sites and i see no errors. i can insert template like in version tinymce < 7.

[thet]

Does the TinyMCE license allow us to use the TinyMCE 6 plugin in TinyMCE 7?
If yes, I'm fine with merging this.

[petschki]

TinyMCE lincense is GPLv2+ ... since the "old" template plugin is distributed as "open source plugin" I assume it's ok to use the code ... we have to maintain it ourselfes anyway if it doesn't work anymore in a future tiny release. https://www.tiny.cloud/docs/tinymce/6/template/