Code conventions formalization

[Nir Lisker]

Hi all,

As we're getting closer to 12 and the GitHub repo is gaining traction, I
think we should start formalizing in writing the exact code conventions we
want to use to decrease future mess. The wiki has some rules [1], but there
are areas which are still fuzzy. The check tools could also use an update.

Just a few specific points:

* Line length limit vary greatly even withing the same class.
* Number of empty lines before and after closing bracer `}` of classes (and
inner classes) varies.
* Annotations sometimes appear on the same line and sometimes above what
they are annotating.
* I recommend we enforce using @Override wherever applicable, it can only
help.
* Usage of 'var' (should probably link to the style guide by Stuart Marks).

After we decide on what we care about and in what way, we should supply a
formatter for each IDE (either in the repo or another source) so that
contributors can easily plug it in and get everything right.

- Nir

[1] https://wiki.openjdk.java.net/display/OpenJFX/Code+Style+Rules