Transitioncontroller rework: Split up task actionmenu in to regular and agency one

Fixes #479.

Completely rework task and forwarding transitioncontroller guards:
 - introduce Conditions helper class
 - Define complete tests (dropping Mocktest's :tada:)
 - Simplify
 - Provide agency differentiation, use to split up the task actionmenu in regular and agency transitions.

@deiferni 

@phgross please use http://docs.sqlalchemy.org/en/rel_0_7/core/expression_api.html?highlight=like#sqlalchemy.sql.operators.ColumnOperators.startswith