Solve split package problem and make jpms modules

[PavelTurk]

Currently, JediTerm doesn't support JPMS as core and ui modules have split packages, for example com.jediterm.terminal what makes it impossible to use them on JPMS.

I suggest to solve this problem and create two separate JPMS modules - core and ui.

We ported JediTerm to JavaFX with JPMS, see this link and although we didn't modify origin core module we have to support it. So, solving this issue will help us a lot.