Periodic media

[sulheim]

This PR adds the possibility to write periodic medium parameters into the layout file.

There are two settings: global and detailed.

• global set the same periodic media to all cells in the layout, function setGlobalPeriodicMedia
• detailed set the periodic media to a specific cell in the layout setDetailedPeriodicMedia

There are currently only five different periodic functions to choose from, but this can easily be extended in the comets software. The functions are:

• step: A normal step function (i.e. on/off)
• sin: Sinus function
• cos: Cosinus function
• half_sin: max(sin, 0), i.e. a sinus function when above 0. Used to model diurnal light conditions
• half_cos: Similar to "half_sin", but with cosinus.

All functions must be provided an amplitud, period, phase (not angular phase) and offset.