Allow areas to be optionally open to all other users

In other words, you can retain ownership of an area but disable and
re-enable the protection aspect at will, via the area_open chat command.

By default, nothing is any different following this commit - all
existing areas are protected, as are new ones. But you can do (for
example) "area_open 1" and if you're the owner of that area, it's
now possible for other users to interact there. "area_open 1" again to
toggle the protection back on.

Where there are sub-areas, the main owner and ALL sub-area owners at a
particulare location must have set the areas to open to disable
protection.
Allow protection of intersecting sub-areas and make error message more informative
Allow open areas inside closed areas to be used openly
Allow areas to be optionally open to all other users

In other words, you can retain ownership of an area but disable and
re-enable the protection aspect at will, via the area_open chat command.

By default, nothing is any different following this commit - all
existing areas are protected, as are new ones. But you can do (for
example) "area_open 1 yes" and if you're the owner of that area, it's
now possible for other users to interact there. "area_open 1 no" to
switch the protection back on.

Where there are sub-areas, the main owner and ALL sub-area owners at a
particulare location must have set the areas to open to disable
protection.
Show area names on hud
Add api function to find nearest area
Fix various readme typos