update version to 3.0.0

allowing turning off local collections; further ES6ification; v3.0.0-…

…alpha.1

updating code to ES6+, making API just a bit nicer, updating use of P…

…romises to ES6 standard, allowing plugging in WebSocket implementation etc

Release for DDP version pre1 introduced in Meteor 0.5.7

Meteor versions <= 0.5.6