Using parameters in expressions

[pl0xz0rz]

This PR:

• Allows the use of select widgets for variables in anonymous expressions - TODO: Do this also for aliases
• Fixes an infinite loop in unweighted quantiles if the interval consists of all NaN

[miranov25]

Missing parts:

• adding support for units (constant)
• support for the axis names should be used via user custom names
  • xAxis={varY} {varYNorm}