Add HED validation to EEG2BIDS

[christinerogers]

@jeffersoncasimir can provide more details

[jeffersoncasimir]

The hedtools python library should be imported and relied on for the validation of HED tags in events.tsv and events.json files.

Documentation: https://hed-python.readthedocs.io/en/latest/

[christinerogers]

no new tab, just find a way to display in the in the 3) rd tab
after user provides input in tab 2, just before file is converted, so errors can be flagged and converted
display error or warning : invalid HED 8.3.0 tag

• additional events files -> check these and idsplay any issues

8.3 HED required for eegnet

to ocnsider also: the independent bids-validator in the last tab could also benefit from checkign hed tags.

jefferson to walk Nada through when she's ready:

• can look up in the header which schema is uesd
• check against that schema
• jefferson to check that sufficient warnings are there for EEGNet which only 8.3.0