DATAMONGO-941 - Add support for Update $min.

[christophstrobl]

We now offer dedicated methods for min (Number/Date) on Update.
As BigInteger and BigDecimal values are converted to String before storing in MongoDB it is not possible to use for the min operation. Therefore we type check both the given value and the property it should be applied to and raise an error if it fails.

This PR ist a first draft for discussion and should not be directly merged.

[thomasdarimont]

Rebased on master and adjusted the PR quite a bit.

[thomasdarimont]

I adjusted the PR accordingly - any other issues?

[odrotbohm]

The changes to the QueryMapper look rather involved. When I suggested the Keyword to take the responsibility for validating I was rather assuming something like this:

class Keyword {

  // might need additional parameters
  void validate(PersistentProperty<?> property, Object value) {}
}

A factory method for keywords could now either use the non-validating default instance or detect things like $min or $max to use a dedicated subclass (e.g. ComparableValueEnsuringKeyword) that would instantaneously reject the value if it doesn't match the implemented requirements.

Am I overseeing something that justifies the additional complexity?

[christophstrobl]

I did an alternate approach without Validators in an another branch. We still can move the verification to Keyword - thoughts?

[mp911de]

Superseded by DATAMONGO-1404 and #353.