Add EasyBind.concat(List<ObservableList<T>>)

[maul-esel]

Creates a new list that combines the values of the given lists. Unlike FXCollections.concat(), updates to the source lists propagate to the combined list.

I needed this for a project of mine, so I hacked it together. Since it might be useful to others as well, I thought I'd submit it here. If there are any changes you'd like me to make, let me know.

[TomasMikula]

Thanks for the PR!

OMG, I didn't expect FXCollections.concat() to be so silly!

I can see how your implementation would fail on

concat(list, list);

Some tests would be nice.

[maul-esel]

I added some tests, hope they're ok. Otherwise let me know.

I also added a short test for concat(list, list); and so far it seems to work. What part exactly did you expect to fail? (maybe I didn't cover that)

[TomasMikula]

You did not test that the published change events are correct.

[N247S]

Just as an idea, wouldn't it be better (for boilersplate's sake) to switch out the sourceLists field in ConcatList with a plain array? As it's immutable, and operations performed on the List are easily done as array operations (This would also means the concat method in EasyBind can be merged into a single varargs method).

Second (for performance sake), would it be an idea to cage the overal size? As it can be detected when the underlaying lists are changing, it would easy to refresh/recalculate the overal size (or at least set a flag that the current size is invalid), whichever way is prefered.

[tobiasdiez]

Since this project sadly doesn't seem to be active any more #16, I've created a fork and continued development there: https://github.com/tobiasdiez/EasyBind.

I liked your changes in this PR, and thus included them in the forked repo. Hope this is OK for you.