move transaction mgmt into TransactionManager

This will fail one unit test due to wrong stubs/mocks. Will convert
TransactionManager into something more akin to an "Era" later on --
this should make testing easier again.
A TransactionManager should be a (functional) View/Era

This starts a rather long-winded refactoring that should make the code
base better readable (sooner or later).

The basic Idea is, that an View/Era/TransactionManager can add new
Transactions. If a new era starts, it starts with a blank slate.
bump version for beta release