Notification of string changes

Author: Sara Arjona
MDL-61215 core_files: add new optimised_image group
Currently, PHP getimagesize method doesn't support SVG images.
As some features, such as badges, processs and optimise the images
before using them, a new filetype group has been created to exclude
SVG from there: optimised_image.
SVG can't be removed from web_image because then users won't be
able to add SVG images to their courses using labels, pages...


http://git.moodle.org/gw?p=moodle.git;a=commit;h=c6bd7bd0aba415cb52f0089e1de42eaaa61a531a
http://github.com/moodle/moodle/commit/c6bd7bd0aba415cb52f0089e1de42eaaa61a531a

+ 4.0 en [group:optimised_image,core_mimetypes]