Remove all proposal-related code

We're not using proposals at the moment, so it's just in the way.

app/models/proposal.js

@@ -1,32 +0,0 @@
-import EmberObject from '@ember/object';
-import { alias } from '@ember/object/computed';
-import bignumber from 'kredits-web/utils/cps/bignumber';
-
-export default EmberObject.extend({
-
-  // Contract
-  id: bignumber('idRaw', 'toString'),
-  creatorAccount: null,
-  contributorId: bignumber('contributorIdRaw', 'toString'),
-  amount: bignumber('amountRaw', 'toNumber'),
-  votesCount: bignumber('votesCountRaw', 'toNumber'),
-  votesNeeded: bignumber('votesNeededRaw', 'toNumber'),
-  executed: null,
-  ipfsHash: null,
-
-  // Shortcuts
-  isExecuted: alias('executed'),
-
-  // IPFS
-  kind: null,
-  description: null,
-  details: null,
-  url: null,
-  ipfsData: '',
-
-  init () {
-    this._super(...arguments);
-    this.set('details', {});
-  }
-
-});