Load signer from the contract

[biern]

• [x] PS Contracts API
• [x] Minimal test data
• [x] Populate test data with npm start
• [x] Populate test data for e2e testing
• [x] E2E test
• [x] Clean it up

[biern]

@jstefanski I still need to do some cleanups here, but in case it's blocking your work this is how I've solved the testrpc / seed / contracts deployment / rpc fixtures in e2e environment issues: https://github.com/SignHash/signhash-webapp/pull/24/commits/515497831850e735ed141db6ef7d757fdab681c0 It seems pretty solid to me.

[jksf]

I fixed typos, I will merge it as soon as it passes CI (just in case :-)).

Next, I will work on migrating NPM script to use signhash-contracts NPM package instead of git and new seed script.