Drop support for IE6

If you grep the code for IE6, you'll see that there are a lot of pages that include hacks for IE6. XWiki should not support or encourage the use of IE6 because Microsoft stopped fixing its security holes in April 2014.[1] Anyone who is still using IE6 is at risk of security breach and data theft. Meanwhile, up-to-date browsers are being slowed down by having to download and process the IE6 code.

Please speed up XWiki by removing support for Internet Explorer 6 and under. At the same time, support can also be removed for Firefox 44 and under, as those versions are not receiving security updates anymore either.[2]

This request is consistent with, and more conservative than, XWiki's stated policy of no support for Internet Explorer 9 and under.[3]