User should be allowed choose an arbitrary field delimiter

I have a file where fields are delimited by a ":". I can open them in Table Tool changing every occurrence of ":" to "|", but in my opinion the user should be allowed to choose an arbitrary field delimiter.

No files or tests are named. Start by locating the CSV file-opening and parsing entry points in the Mac application, then trace where the current field delimiter is fixed. Done means users can choose a delimiter such as ":" when opening a file and the resulting fields are split correctly.

Written by the indexing model from the issue text.