Use thread-safe queue for tooltips

[Swedz]

I only have proof it has happened with my similar tooltip system, but MI uses a PriorityQueue to store the tooltips for items (see here) and EMI will try to load tooltips asynchronously over multiple threads which can cause a ConcurrentModificationException in MITooltips.attachTooltip (here). Here is the issue i opened on my mod doing a similar thing if you want to see the stacktrace. Not sure if this is just a me thing, since I've only ever seen this happen once and it was with my mod but thought I should give you a heads up.

[Technici4n]

I wonder how applicable this is to how MI currently operates. If all the tooltip attachments get registered in the same class, the registration is protected by the class initialization lock.