[SECURITY] Escape caption of media using css_styled_content

[SECURITY] Escape caption of media using css_styled_content

The caption must be escaped. As this is only a textarea, the parsefunc
is not needed.

Furthermore, the fields "altText" and "titleText" use htmlspecialchars instead of stripHtml.

Resolves: #41690
Releases: master, 6.2
Security-Commit: 2cfa39c452a35286deffdac4f0a03314e6f6ee69
Security-Bulletins: TYPO3-CORE-SA-2015-010, 011, 012, 013, 014, 015
Change-Id: I17a43cfa860c058054cd73f6ab751edfa91a02ce
Reviewed-on: https://review.typo3.org/45284
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>