Clarify usage of UTF8 encoded captions/quantities from extractors

[ghorwin]

TSV and DataIO containers (as well as new btf binary files) contain quantity description strings. In DataIO this relates to the QUANTITIES field, in tsv and btf this is the entire header line.

Currently, the series model (Qt) accesses theses strings from ExtractorManipulator library and _expects_ them in UTF8 encoding. Hence, we should require DataIO and tsv/btf files to write there quantity strings in UTF8-Encoding.

In PostProc, we need to change nothing, only add explicit documentation to the file reader and extractor/manipulator classes - hence this ticket is only a documentation ticket.

All tools that generate project files (i.e. DELPHIN, THERAKLES, SIM-VICUS) that contain strings to be used in solvers need to ensure that quantities arrive as utf8 values in the data files.

[ghorwin]

Milestone renamed

[ghorwin]

Milestone renamed