Set $wgBlockAllowsUTEdit = true; by default

Set $wgBlockAllowsUTEdit = true; by default

This setting allows blocked users to edit their talk page, unless
talk page editing is specificly revoked in the Special:Block screen.

Almost all Wikimedia wikis do this, to the point where many people
don't even realize it's a config option.

Note: Existing blocks will not be affected by this setting change.

Change-Id: I05194f3fb313098284c474c948d7d26541ab6094