Typed callbacks

This update changes the callbacks so that the value can be any type. Also, the callback IDs are now Longs. Finally, some minor concurrency errors are addressed.

Example usage of typed callbacks:

Dashboard.addInlineListener("SOME_STRING") {
    key: String, value: String? ->
    println("$key : $value")
}

Dashboard.addInlineListener("SOME_DOUBLE") {
    key: String, value: Double? ->
    println("$key : $value")
}

Dashboard.addConcurrentListener("SOME_INT") {
    key: String, value: Int? ->
    println("$key : $value")
}

Dashboard.runIfUpdate("SOME_BOOLEAN") {
    key: String, value: Boolean? ->
    println("$key : $value")
}

Dashboard.addInlineListener("SOME_VARIABLE") {
    key: String, value: Any? ->
    println("$key : $value")
}