- POM: Upgraded version 7.1.2-SNAPSHOT -> 8.0.0-SNAPSHOT
- POM: added owasp-dependency-check plugin
- POM: removed dependency koloboke
- Implemented extension mechanism to switch HashMap/HashSet
implementation from default Guava/native Java to others (implementations
to be provided by external modules) such as Koloboke
- Renamed classes: ValueExpression -> ConstantExpression
- Changed Expression interface: method boolean isStatic() replaced by V
getValue() to get the constant result if expression is constant
- Changed Function interface: now extends AtomicValue (new class which
extends Value) like AttributeValue instead of Expression
- Changed ExpressionFactory to return FunctionExpression (new class)
instead of Function where applicable
- Changed FirstOrderFunctionCall to interface and moved logic to
BaseFirstOrderFunctionCall
- Changed DatatypeFactory interface: removed method isExpressionStatic()
now useless since we have Expression#getValue() 
- New class PrimitiveDatatype for primitive value datatype
- Added FUNCTION_DATATYPE (function datatype since Function now extends
AtomicValue therefore Value) to StandardDatatypes