* Move pkhex.drawing calls out of form constructors
designer doesn't like it; if Main can't be designed then there's some
call that it can't process for whatever reason
* Add netcore3 targeting
Closes#2198 by adding a netcore3 build option
Closes#2391 by retaining designer functionality and net46 builds
Closes#1236
pk4/bk4 only, obviously
side note, using static events is no-no, designer auto-removed them.
just manually reapply (as well to others that used it)