Split code into core and submodules for non-core code

[ctadlock]

The first commit for this merge request. DO NOT MERGE YET

Items:

• Split project into parent and submodules
• Moved all code into tornadofx-core submodule
• Completely rewrote the pom.xml files
• Did not move over test code; I think this should be reviewed first
• Did not move over documentation via dokka; not sure how this works yet

[ctadlock]

https://github.com/edvin/tornadofx2/issues/3

[ctadlock]

@edvin Take a look at this for the structure; you should be able to pull it down and use it. I was able to use it in our app without any issue. If youre OK with this, can then work on moving the components out of core into their other projects.

[ruckustboom]

I converted this PR to a draft/WIP to prevent accidental merging. When you're ready for it to be merged, mark it as "Ready for review".

[ctadlock]

I converted this PR to a draft/WIP to prevent accidental merging. When you're ready for it to be merged, mark it as "Ready for review".

Thanks. Ill be the one to merge it anyways, but good to follow the right process.

[ctadlock]

Going to merge this in and start moving forward...