NF: Adding data file separator to expInfo

[EitanHemed]

This comes to solve issue #5141, a feature-request to be able to pass the data file separator to psychoJS (currently uses only comma).

The changes proposed here should be reviewed alongside this modification.

[TEParsons]

See my comments on the accompanying PsychoJS PR for feedback on using a field in expInfo

It's also worth noting that this would only appear in the compiled Python code - the functions to write JS code all end with JS (e.g. writeInitCodeJS)

[TEParsons]

Looks great! The test suite is failing because you're using the Param object to index delim_options rather than its (string) value - easy mistake to make and very easy to fix. I'll submit a fix to your branch, once that's merged I'm happy to pull in both this and (pending approval from the JS team) the accompanying PsychoJS PR

[TEParsons]

Oh, never mind, looks like I can push directly to your branch... So yes, once the accompanying PsychoJS PR is approved I'll pull this one in too :)