Ability to submit proposals using only quill

[jwiegley]

Description

This changes allows one to submit motion proposal directly using quill, rather than having to involve dfx. Usage:

quill neuron-manage <neuron-id> --proposal-title "<title>" --proposal-summary-file <summary file path>"

How Has This Been Tested?

I will test it tomorrow by submitting a motion proposal. Until then, this is marked draft.

Checklist:

• [ ] I have made corresponding changes to the documentation in src/docs.

[jwiegley]

I've used this myself to submit a proposal.

[jwiegley]

That Windows failure is going to make it impossible to test using proposal contents from a file via this CI.