update to mongo changes in 0.31
review log config to follow changes in restx 0.31
upgrade to restx 0.31-SNAPSHOT and add log admin module
errors: review API: use a provided UUIDGenerator instead of "current" one [BREAKING]

This required to introduce a RestxErrors component and use it to create RestxError,
instead of using a static method.

So when you used to do `RestxError.on(sg)` you now have to do `errors.on(sg)` where
`errors` is a `RestxErrors` field that you get injected.
security: introduce new classes to help implement authenticator

it should now be easier to implement an authenticator following good
security practices.

it also provides a very simple file based user repository which can be used
for prototyping / simple cases where users can be managed outside the app.
security: CredentialsChecker is now CredentialsStrategy

and provides encryption too, not just checking.
use new JongoUserRespository
update to restx 0.31
Merge pull request #1 from xhanin/restx-0.31

Restx 0.31