Nicely handle running out of columns in the new-project wizard

As mentioned in #208, when using the new-project wizard, if the data file has only 2 or 3 columns, but the user says yes at HasLanguageStep and/or HasSpeakerStep and we run out of columns, the SelectXStep crashes.

Solutions: rewrite the column selection step as a single larger step showing all the columns and letting the user pick the basename/text/language/speaker from the list of all columns.

E.g., maybe
```
Flag each column with its contents, from b: basename, t: text, s: speaker, l: language. b and t are required, use s and/or l only if your filelist has a speaker and/or a language column.
[ ] fichero
[ ] texto
[ ] idioma
[ ] vocero
```
which would get filled like this
```
[b] fichero
[t] texto
[l] idioma
[s] vocero
```

This idea would make sure the user cannot paint themselves into a corner and run out of columns, and it makes it cognitively simpler: they know up front all the columns we will be asking about.