Turn Adapt wait interface into a hard API from events

[oliverfoster]

This arose from the naming of the callback event, "plugins:ready" - which suggests that the plugins are ready, singularly.

This mechanism is actually to stop adapt performing long blocking operations on initialization and navigation. Providing an interface to force Adapt to wait for asynchronous operations to take place before proceeding.

This idea is to turn:

Adapt.on("plugins:ready", function() {
    console.log("output3");
});
Adapt.trigger("plugin:beginWait");
_.defer(function() {
    console.log("output1");
    Adapt.trigger("plugin:endWait");
});
Adapt.on("plugins:ready", function() {
    console.log("output4");
});
Adapt.trigger("plugin:beginWait");
_.defer(function() {
    console.log("output2");
    Adapt.trigger("plugin:endWait");
});

Into:

Adapt.wait.queue(function() {
    console.log("output3");
});
Adapt.wait.for(function(end) {
    console.log("output1");
    end();
});
Adapt.wait.queue(function() {
    console.log("output4");
});
Adapt.wait.for(function(end) {
    console.log("output2");
    end();
});

Also included are:

Adapt.wait.isWaiting();

// Increments count for waiting queue
Adapt.wait.begin();

// Decrements count for waiting queue
Adapt.wait.end();

// Resolve asynchronously when the queue count is brought back to 0
Adapt.wait.queue(function() {

});

// Performs, begin, callback and end
Adapt.wait.for(function(end) {  
    end();  
});