[FEAT]: custom extension

[glebsts]

Description

Hello, thank you for nice and easy to use plugin!
One thing I miss is inability to match additional extensions that should be processed as keystores. E.g. we use "truststore" as extension. E.g. for custom editor templates I can setup list of extensions that should be treated as belonging to certain language. E.g. I have *.groovy, *.Jenkinsfile for Groovy interpreter.
Would be awesome to have simple GUI to configure extensions that should be opened with SSL Toolbox.

Additional Information

integrating with IntelliJ file extension registry?