(bug 8440) Allow preventing blocked users from editing their talk pages

(bug 8440) Allow preventing blocked users from editing their talk pages
* Adds database field to ipblocks table, ipb_allow_usertalk, storing whether or not the user can edit their own talk page. Defaults to 0 to coincide with the default value of $wgBlockAllowsUTEdit.
* Recommended to update all current blocks to have a allow_usertalk value of whatever the current setting is
* Retasks $wgBlockAllowsUTEdit to be the default value of the field in the blocking screen - unless a sysop changes the checkbox, will use whatever that variable is set to.