Library should check proposal data validity *before* `gobject prepare` command

[riongull]

Before the production release let's make sure the library itself checks proposal data for validity before it gobbles the 1 DASH with gobject prepare command. Right now it can make a successfulgobject prepare tx that then fails on gobject submit.

Example bad proposal name that succeeds making the 1 DASH tx but fails gobject submit:

let isoDate = new Date().toISOString();
let proposalName = `proposal_${isoDate}`