Refactor web3 initialization

This changes how we wait for web3 and accounts to be available and
renames web3Provider to ethProvider as we could be able to swap the
different providers (ethers.js vs. web3)

app/components/add-contributor/component.js

@@ -20,7 +20,7 @@ export default Component.extend({
   isValidAddress: function() {
     // TODO: add proper address validation
     return this.get('newContributor.address') !== '';
-  }.property('kredits.web3', 'newContributor.address'),
+  }.property('kredits.ethProvider', 'newContributor.address'),
 
   isValidName: function() {
     return isPresent(this.get('newContributor.name'));