[Typo3] Proper e-mail encoding for extensions

[Jan Bednarik]

> Hi Jan,
Hi again,

here's a part of e-mail sent by this modificated class:

This is a multi-part message in MIME format.

------------part_1_42a601238b01c
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: base64

Sk1FTk86ICDFocSNxZnFv...

------------part_1_42a601238b01c
Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: base64

PHRhYmxlIGJvcmRlcj0iMCIgY2VsbHBhZGRpbmc9IjIiIGNlbGxzcGFjaW5nPSIyIj48dHI+PHRk
IGJnY29sb3I9IiNlZWVlZWUiPjxmb250IG...