Make app.configure async aware

[AuHau]

I am not completely sure, but I believe that app.configure() is Feather's addition to Express right? On Express's side, the app.configure was removed since version 4.x which I believe you are using latest version for the @feathers/express package right?

If that is the case I would like to suggest to make the app.configure() async aware. Preferably if Promise is returned by the callback await until its resolution.

This is important when you want to configure your application from async sources (for example populate some data-stores from database etc.). This would for example "fixed" the need for storing Promise on app when syncing database for Sequelize like app.set('sequelizeSync', sequelize.sync()).

This I believe should not be a breaking change. Would that be something you would be willing to accept? If so, I could provide PR for this functionality.

[daffl]

Asynchronous setup and configuration is slated for the next version. The original issue is #509

[AuHau]

That is pretty dope! Thanks for the info!
Looking forward to the new release :-)