add backup service
extract backup into service
added auto backup after create/join
add tests
Fixes on storage tests (removes current localStorage)

* Fix test that removes localStorage (made clean() function).
* Enable the test for LocalPlain model.
Merge pull request #686 from maraoz/automatic/backup

Automatic backup after create/join
Merge pull request #687 from cmgustavo/bug/test-storage

Fixes on storage tests (removes current localStorage)
make mocha browser tests all run with no console errors

...except Wallet and WalletFactory.
make Wallet tests work in mocha browser
make WalletFactory tests work in mocha browser
add TxProposals test; fix WalletFactory link
fix karma tests

by using require('sinon') not incorrect require('../sinon')
fix more tests broken in last rebase
fix tests
Merge pull request #681 from ryanxcharles/bug/fix-mocha-browser-tests

make mocha browser tests all run with no console errors
fix conflics