bug 10158 : do not mention allowing others to contact you if $wgEnableUserEmail=false

bug 10158 : do not mention allowing others to contact you if $wgEnableUserEmail=false

This required to tweak HTMLForm to support an array of message keys
for help message. I could reuse help-message but since this helper
also supports array, I created an additional helper for array of
messages.

To test use variations of $wgEnableUserEmail and $wgEmailConfirmToEdit.

Path adapted from jopiswezggzmw at mailinator dot com