Allow configuration to be modified after the SDK is instantiated

[justincy]

Presently all configuration has to be provided up front when the SDK is instantiated. Let's add the ability to modify the configuration after creation.

Are there any options that shouldn't be changed?

[justincy]

// Set multiple options at once
client.config({
    appKey: 'KEY',
    redirectUri: 'http://foo'
});

[justincy]

2baf1ff