Clean up duplicated code.

ShadowMapLinear and ShadowMap did almost the same thing.
Remove the added delta, which is not needed for exponential shadow maps.
Add rain effect UBO parameter.

It is currently not yet used.
Fade to gray sky for rainy weather
Decrease shadow strength when raining
Add some ambient light when raining
Add weather simulator

It is not used yet.
Merge branch 'master' of github.com:larspensjo/ephenation-client
Create a flag to force windowed mode
Removed class TemporalReprojection

It is not really needed.
Merge branch 'TemporalReprojection'