Inject contents of `<head>` tags into composer's head section. Also overwrite `DOCTYPE` and all `<body>` attributes

Involved are DOCTYPE, html, head and body Tags. If I delete the standard TB HTML Code and copy my own HTML Code in an new E-Mail in Thunderbird everything works perfekt. If I use ST4 im getting a really mess. Code Sample enclosed. Hope, this get solved :) 
[ST4.Code.Sample.txt](https://github.com/RealRaven2000/SmartTemplate4/files/4981654/ST4.Code.Sample.txt)
