App connectors: define a named export alongside the default

[bpierre]

The same way @aragon/connect exports default and connect, app connectors should export default (which they do already) and a corresponding named export, e.g. connectVoting and connectTokens.

This will allow to be imported from Node using an explicit default (or from our side, it would avoid mixing all our named exports on e.g. connectVoting() as it could create conflicts).