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'
Use reference instead of pointer for SetSingleTarget()
Should not be used from gameDialog, so it can be private.
Draw extra stereo frame when computing shadow map
Move viewport settings out of gameDialog::UpdateProjection
Simplify SetViewport()
Remove common.OvrDistortion from shaders where it wasn't used
Move barrel distortion from SimpleTexture to its own class

Take it away from common.glsl, as it is not used commonly.
Prepare the barrel distortion shader for using local uniforms

Instead of the parameters in the UBO.
Move distortion control from common uniform buffer to barreldistortion
Add extra drawing of screen after left eye render

An old texture is used, making the display flitter
Best yet, but doesn't look good when looking downwards.