New weather implementation

[Madecu]

Description

• Added a new script in PythonAPI/util to be able to change the sun position and the weather parameters individually.
• Activated Mesh Distance Fields.
• Changed cloudyness for cloudiness.
• Added three new parameters for the weather (Fog density, Fog distance, and Wetness).
• New function "SetWeather" in weather.cpp to be able to update the weather parameters without notifying it to the blueprint's event.

Where has this been tested?

• Platform(s): Windows and Linux
• Python version(s): Python 3.7
• Unreal Engine version(s): 4.22

Possible Drawbacks

No drawbacks found yet.

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This change is 

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would update our CHANGELOG.md based on your changes.

[marcgpuig]

Reviewed 5 of 7 files at r1, 2 of 5 files at r6, 1 of 1 files at r9, 4 of 4 files at r10.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @bernatx)

[bernatx]

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @bernatx)

[jahaniam]

Mesh Distance Fields was disabled to remove ghosting effect! #1838

[Madecu]

Hi @a-jahani

We decided to enable Mesh Distance Fields again to improve the lighting in our scenes. We still have some ghosting but we managed to minimize it as much as we could. On the other hand, we gain a much better looking with Distance Fields Ambient Occlusion and Distance Fields Shadows combined with Cascade Shadows.
If the ghosting is still an issue, the user can always disable it. We will explain it how in the 0.9.8 release documentation.