1. Do not update physics and animations for actors outside processing range (bug #4647)
2. Do not render such actors
3. Add transparency to actors near processing border, so they will not pop up suddenly
This makes it possible to "reload" the Ptrs in active cells when changes happen to the ESM record that they are based on. In practice, the old Ptrs are deleted, their RefNums and MpNums are blanked out, and new Ptrs are created that use the same RefNum and MpNum as before.
The above has required me to also add a method called setRefNum() to CellRef to allow setting a RefNum on the fly.
There may be a more elegant implementation available for updatePtrsWithRefIds(), but it requires additional research.
Although weather sync was added by Koncord to the rewrite in fd721143e2 in a way that used surprisingly few lines of code, it relied on the server requesting weather states every second from authority players and sending them to non-authority players, while also allowing only very sudden weather transitions across regions, i.e. if there was one player in the Ascadian Isles who had stormy weather, and another player with clear weather in the Bitter Coast Region walked across to the Ascadian Isles, that player was instantly made to have stormy weather with no kind of transition at all.
My approach solves both of those problems. It solves the packet spam by only sending weather updates to the server when weather changes happen or when there are new arrivals to a weather authority's region, and it allows for both sudden weather transitions when players teleport to a region and for soft, gradual transitions when players walk across to a region. It is inspired by my previous actor sync, and uses a WorldRegionAuthority packet to set players as region authorities in a similar way to how ActorAuthority sets players as cell AI authorities. Weather changes are created only by the region authority for a given region, and weather packets are also only sent by that authority.
However, it should be noted that gradual weather transitions are used by default in this implementation. To use sudden weather transitions, the serverside Lua scripts need to forward WorldWeather packets with the forceWeather boolean set to true. That is, however, already handled by our default Lua scripts in situations where it makes sense.
Prevents compiler warnings such as this:
```
/Users/Will/CLionProjects/OpenMW/apps/openmw/mwgui/windowbase.hpp:65:22: warning: 'onOpen' overrides a member function but is not marked 'override' [-Winconsistent-missing-override]
virtual void onOpen();
^
/Users/Will/CLionProjects/OpenMW/apps/openmw/mwgui/windowbase.hpp:38:22: note: overridden virtual function is here
virtual void onOpen() {}
^
```
