Add function to get all layers that references a project item

[Rune Gangsø]

Currently you have to this:

forEach( item.usedIn, function ( comp ) {
    forEach( comp, function ( layer ) {
        if ( layer.source === item )
            // Do something
    })
})

It would be nice have something like this:

var layers = aeq.getItemLayers( item )

[Former user]

+1

[Rune Gangsø]

Add getItemInComps

Resolves #26

→ <<cset 43be96d420e5>>