New features added to lap- and segment-based math functions

Now evaluation of a subexpression is supported instead of evaluation a channel only:

LapAve((speed_wl + speed_wheel_r) / 2)

An optional argument was added to all lap- and segment-based math functions:

LapAve(<channel>)-> LapAve(<expression>[;<condition>])

Only values are taken into account, if the condition evaluates to true.

Note: Because these math functions have to evaluate their subexpressions independently from the calculation of the math channel, the use of variables within the arguments is not allowed!