remove synchronous APIs

[gr2m]

• [x] remove hoodie.account.username
• [x] remove hoodie.account.id
• [x] remove hoodie.account.isSignedIn()
• [x] remove hoodie.account.hasInvalidSession()
• [x] make [hoodie.account.get](https://github.com/hoodiehq/hoodie-account-client#accountget()) asynchronous, fetch data from remote like current hoodie.account.fetch unless options.local is true or user is not signed in
• [x] make [hoodie.account.profile.get](https://github.com/hoodiehq/hoodie-account-client#accountprofileget()) asynchronous accordingly
• [x] remove hoodie.account.fetch
• [x] remove hoodie.account.profile.fetch
• [x] remove hoodie.account.ready
• [x] hoodie.account.get: implicitly set options.local to true if only id and session.* properties are requested

closes #139. closes https://github.com/hoodiehq/discussion/issues/114