Taught it how to accept insert requests, and how to delete an existing
algorithm/sequence from the sequence.

Did not introduce a __delitem__ function, since Athena configurables
don't have such a function defined on them either.


Former-commit-id: 6f8fbf4af3f4c3904d541e2d06c37ebc2dd9f9c3

In order to be able to construct a bit more elaborate algorithm
sequences using exactly the same code for Athena and EventLoop, taught
the standalone version of AlgSequence how to swallow and then handle
AlgSequence objects added to it.

Added a bunch of unit tests to the code at the same time.


Former-commit-id: c57d4e0efd730663ecffaa8bf574e1b5e9b7e7c2

They differ quite a lot still, but this should allow us to compare standalone
and Athena configurations a little bit more easily.


Former-commit-id: 43a7964461114dcc64128078fcb82805c2aa982a

The AnaAlgorithm.AlgSequence class is just meant to emulate Athena's
AthSequencer class for EventLoop. (In Athena mode the user is given
the AthSequencer class when importing this code.)

Most of the development will go into the AnaAlgorithm.AnaAlgSequence
class, which is a common layer above the Athena and EventLoop implementations
of the algorithm sequence. Providing helper methods for correctly
configuring an analysis algorithm sequence.


Former-commit-id: fd409a8d2e85c8569d43c8b723d0dab70753121b