Fix #7847: Use ViewportSign coordinates for sign Kdtree coordinates (#7849)

Ensure the same coordinates are used for station/town/player signs regardless of how the landscape changes below it after the coordinates were first determined.

By keeping track of whether each ViewportSign is valid for Kdtree use (and only ever registering the viewport sign when the object is valid) a lot of code can be simplified and become more robust at the same time.

(svn r19956) -Fix: close list of vehicles with given oil rig in orders when the oil rig is deleted
-Fix (r19952): close the list when it is not sticky

(svn r16909) -Fix [FS#2996]: NewGRF stations would be triggering assertions all over the place when using the more advanced station types.
-Change: make (rail) waypoints sub classes of 'base stations', make buoys waypoints and unify code between them where possible.

(svn r15589) -Fix: drawing of waypoints with invalid owner was broken
-Change: don't take over waypoints without owner, it could belong to a bankrupted company (and the code was broken) - savegame conversion code is a bit more liberal now, too

(svn r14958) -Codechange [FS#1923]: when checking for unique names, compare only with manually set names
There are situations that aren't solvable (because of different language files), so if the user really wants to have duplicated name, allow him to do so. It solves desyncs between server and clients using different languages. It behaves the same in SP and MP, so users won't see the different behaviour as a bug (and even checking in SP could be worked around by the user).

(svn r13251) -Codechange: rename _patches to _settings as that is more logic.
-Codechange: move all Settings into substructs of _settings in a way that they are logically grouped.

(svn r11822) -Codechange: Replaced fixed size custom name array. Names are now attached to their object directly and there is
no limit to the amount of names.
-Fix: NewGRF engines could not be renamed.

(svn r11802) -Fix [FS#716]: do not crash trains when leaving depot to a very long track
-Codechange: use dedicated pathfinder for signal updating, resulting in better performance and possible future improvements