Feature/filter max value

Added a new filter to record the max/min at each quadrature point during time-stepping and output the "max/min" fields.

It is designed for compressible flows but should work for all cases (the fields need to have the same length).

A compressible flow case is tested.

This filter can be used to obtain the amplitude of instabilities. So it would be helpful to get the n-factor.

Preferably to be merged after the time-dependent wall BC.