Support nomemory/java-bean-validation-extension

[pfichtner]

https://github.com/nomemory/java-bean-validation-extension

..or is this already done because these are all custom validations?

[pfichtner]

depends on #87
see e.g. https://github.com/nomemory/java-bean-validation-extension/blob/master/src/main/java/net/andreinc/jbvext/annotations/digits/validator/MinDigitsDoubleValidator.java