This commit adds support for role mapping expression dsl.
Functionally it is similar to what we have on the server side
except the rule evaluation which is not required on the client.

The role mapper expression can either be field expression or
composite expression of one or more expressions. Role mapper
expression parser is used to parse json dsl to list of expressions.

This forms the base for role mapping APIs (get, post/put and delete)

Removed individual expression classes, simiplified
the usage using builders.
Now there is FieldRoleMapperExpression for Field types
(USERNAME, GROUPS, METADATA, DN)
and CompositeRoleMapperExpression for Composite types
(ALL, ANY, EXCEPT)