What this MR does / why does DuMux need it:
Moves all experimental classes/header into a subfolder experimental which mimicks the dumux folder structure. This avoids confusion between experimental and non-experimental headers and also separates testing of experimental features.
Before you request a review from someone, make sure to revise the following points:
\n character. Make sure there is no
\ No newline at end of file comment in "Changes" of this MR.