validation: cleanup

[jknack]

• make constrainctvalidation cast safe
• use config api for properties
  @SentryMan can you look at locales?

[SentryMan]

LGTM, the validator should use the default system locale if none are provided

[kliushnichenko]

@jknack Don't you want to add some .editorconfig to avoid manual code re-formatting? And maybe some contribution guide

[jknack]

we should add it yea. Today it uses spotless + git pre-commit hook that is installed on mvn clean package

[SentryMan]

I'm in the minority, but I use Eclipse, so .editorconfig doesn't do anything for me. Personally, I use the google java formatter to deal with formatting.