Better support for csv-type files

[jepegit]

Using the instrument='something', model='something' is difficult for users. Does a better way exist (that does not require much changes in the code)? At least there should be some easy way for the user to see what the different models can handle and some easy way of tweaking them. Maybe also implement more "automatic" format inspection tools similar to the one that searches for delimiters, etc.

The implementation should be written so that it can easily be moved to v2.0 of cellpy (v2.0 is planned to have a cellpy core with the main procedures that is frame agnostic).