Breaking changes for v2

[franckgaga]

I'm raising an issue to list the possible breaking changes for a future release of a v2 library:

• Removing oracle keyword argument and code in the two legacy.jl files
• Adding the slack $\epsilon$ in the signature of $J_E$ function (to support non-quadratic weighting)
• Consider changing the default arguments of UnscentedKalmanFilter
• Consider changing the default value of transcription in NonLinMPC