Re-implement "Customize entry types" dialog

[tobiasdiez]

In #4716, the Customize entry types dialog was temporarily removed. It should be rei-mplemented in JavaFX once we converged to a stable entry editor layout (refs #2790 #366 #4687 #4688).

[burrbull]

Can I customize them manual?

[tobiasdiez]

@burrbull you can use an older JabRef version (e.g. 3.4.1) to customize the entry types and then use the customized types in the new 5.0 version (only the customization dialog was temporarily removed, not the functionality). Sorry for the inconvenience.

[koppor]

The dialog shows like that:

When working on that, #725 should also be addressed