Signed-off-by: fossabot <badges@fossa.io>

- Upgraded authzforce-ce-core-pdp-api version
- Variables assigned in place of VariableDefinition and set in
EvaluationContext (so far this was done only when first corresponding
VariableReference was evaluated), allowing usage of Variables (not only
via VariableReferences but also) by Attribute Providers
- Simplified TimeRangeComparisonFunction (removed useless setSameDate()
)

authzforce-ce-core-pdp-api
- Changed authzforce-ce-core-pdp-api dependency version

- Change dep authzforce-ce-core-pdp-api: 15.0.0->15.1.0
- upgraded dep authzforce-ce-xacml-json-model: 1.1.0->2.0.0
- Fixed #13:
  - Changed dep mongo-java-driver in testutils module: 2.14.12 -> 3.5.0
  - Idem for jongo: 1.3. -> 1.4.0
- XML StaticRefPolicyProvider type / CoreRefPolicyProvider class:
  - added support for recursive directory searching for policies, e.g.
pattern .../*/*.xml for searching on two directory levels
  - added option to ignore old versions (keep only the latest) when
multiple versions of same policy ID available (ignoreOldVersions=true in
xml config pdp.xsd)
- Simplified for code for detecting duplicate enclosed policy ID/version

Update .travis.yml