[TASK] Change various functions to use utf-8 by default

Many functions in TYPO3core expect a character set parameter to be
defined. Their default was iso-8859-1 in the past and is changed to
utf-8 now.

Change-Id: I9c228821e95167b67811c8475880707d5c77bdb7
Resolves: #34094
Releases: 4.7
Reviewed-on: http://review.typo3.org/9101
Reviewed-by: Michael Stucki
Tested-by: Michael Stucki