Generic CSV importer

[ghorwin]

Add a menu option to "File" menu that allows importing of generic CSV/Text importer and works as follows:

1. read the CSV

• show dialog similar to Word/LibreOffice import wizard where user can select delimiter or none and use fixed column markers
• additional parse options: quotes, trimming of values

• preview of extracted file should be shown in a table preview

2. User select one time 'index' column, or generates an index column according to some rule ("hourly values")

3. User selects columns to import and assigns units (defaults to ---)

4. User selects target directory (empty = default = same as CSV-file)

5. Import settings for this file are stored in a file "filename.extension.p2import" (and read next time the file is imported)

6. import is finished; all columns with same unit are grouped and written into a d6o-file (reference type) each. Project name is set to "filename.extension".

Employ fast csv reader library like:

​https://github.com/ben-strasser/fast-cpp-csv-parser

and show a preview of the data as it would be interpr

[ghorwin]

Not needed - documentation shows meaningful ways on how to get from Excel/Calc to tsv... that should be enough.