Underscores etc. aren't valid in HTML IDs, so escape them properly

Underscores etc. aren't valid in HTML IDs, so escape them properly

This was an issue where a skin's/extension's name would contain spaces,
i.e. "Cologne Blue", "Renameuser for CentralAuth". Such a name would be
passed as-is to the HTML ID, but spaces aren't valid in IDs, and this
would in turn lead to HTML validation issues. Currently the English
Wikipedia's Special:Version page has 26 validation issues and this patch
fixes the supermajority of them.

Change-Id: Ia197b0208fa2abfebbea1cb23f08822db2938162