Change new Fade system much smoother, Speed now up to 40

[s-hadinger]

Description:

Major rewrite of the Fade system for a much smoother rendering.

Now Speed is deterministic and represents the time in half-seconds to move from 0% to 100%.

Example: Speed 4 means it takes 2 seconds from 0% to 100%, and by consequence 0.5s from 0% to 25%.

Other changes:

• Fixed bug that prevented RGB values to go above 25% of brightness (after Gamma correction) if White Blend mode was activated
• changeUIntScale() can now accepts to_min > to_max and compute accurately. This reduces overall code size.

Flash increase: 350 bytes.

Related issue (if applicable): fixes #6942 #3714

Checklist:

• The pull request is done against the latest dev branch
• Only relevant files were touched
• Only one feature/fix was added per PR.
• The code change is tested and works on core 2.6.1
• The code change pass travis tests. Your PR cannot be merged unless tests pass
• I accept the CLA.