Add serial number formatting (#406)

[bennypi]

This is my first shot to add formatting options for serial numbers. It's far from finished, but I would like to get some feedback if I'm heading into the right direction.

Some questions which I had during the process:

• Is X509CertUtil the right place for the formatter interface and enum?
• Where are the other places where a serial number should be formatted?
• Which variants should be implemented?
• Is the look&feel tab the right place for this setting?
• Which rules are used for formatting?

Currently, the enum name is displayed in the preferences. I would add a human readable title, and possibly a tooltip with an example of the formatted serial number.

Feedback is greatly appreciated, don't hold back :)

[bennypi]

Oh well, it seems like accidentally used an really old version for creating the fork and PR. I will close this and redo this on the actual main branch :joy: