perplex data in .dat should use ASCII data instead

[tjhei]

Perplex produces tables in ascii format that are not quite readable by StructuredData loader as they contain extra headers. They are also currently put into a different data structure MaterialLookup / PerplexReader / etc.

Would it be possible to unify these? There are many advantages (MPI loading, saving memory, converting to netcdf, etc)

[Francyrad]

Are Perplex data so heavy that slow the simulation? I used many mbs of tabulated EoS and I didn't see any particular slowness

If there will be changes, please let ASPECT recognize also the "old format", i've dozen of tables and they take time to build...