Rename various onboard_project args and other script names

[TaperChipmunk32]

• Change onboard_project.py to onboard.py
• It would be great to be able to specify a per-user default folder as the source folder?
• Change the argument name to folder rather than --copy-from to remove the hyphen.
• Change --extract-corpora to --extract : I'll ask the other EITL team members to see whether they like this idea or not, since extract_corpora is the name of the existing script. Ideally we'd change the name of extract-corpora to extract.py too.
• Change --timestamp to --datestamp since it's adding a date.
• Change --collect-verse-counts to --countverses and change the name of the collect_verse_counts script to countverses.py

[benjaminking]

Rather than removing all the hyphens, could we instead be consistent about using hyphens instead of underscores (so that users don't need to look up which it is)?

I'd hate to lose the descriptiveness of the parameters, especially when they clarify the role of the argument.