Arcyd: refactor, extract ClassicNaming to module

Continue making way for new naming conventions by moving the
ClassicNaming scheme to it's own module.

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/acceptance_tests.sh
Arcyd: support chaining branch naming schemes

In order to allow users to transition from one branch naming scheme to
another, we will need to support operating under both at the same time.

Add support for compositing branch naming schemes by chaining them
together.

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/acceptance_tests.sh
arcyd/acceptance_tests.sh: extract branch naming

Make it easier to exercise branch naming schemes by extracting the
branch name creation routine into a new, configurable function.

Test Plan:
$ ./testbed/arcyd/acceptance_tests.sh
Arcyd classicnaming: fix collision with r branches

Fix the abdt_classicnaming scheme to not collide with the imminent
r-branch naming scheme, which it will have to share dev/arcyd with.

Add a trivial doctest to ensure 'dev/arcyd/trackers' is left alone.

Test Plan:
$ ./precommit.sh
Arcyd: refactor naming,rm '..review..from_tracker'

Reduce the burden of implementing a branch naming convention by removing
the need for the 'make_review_branch_name_from_tracker()' method.

This work can be done during 'make_tracker_branch_from_name' instead as
the same information is available there.

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/acceptance_tests.sh
Arcyd: refactor naming, rm 'make_review_br.._name'

Reduce the burden of creating a new naming scheme by removing the need
for a 'make_review_branch_name' method.

Instead, provide an example branch name constructed from standard 'base'
and 'description' parameters as specified in abdt_naming.

Test Plan:
$ ./precommit.sh
Arcyd: refactor, 'classic' name defs to globals

Move some definitions out of the 'classic' naming and into the global
scope of abdt_naming so they are re-usable by other naming schemes.

Test Plan:
$ ./precommit.sh
Arcyd: test naming more with 'namingtester'

Make a generalised naming convention tester that will be re-usable for
all new branch naming conventions.

Test Plan:
$ ./precommit.sh
Arcyd: implement the r-branch proposal

Implement a new branch naming scheme to enable the creation of branches
named like this:

  r/base/description

Which is shorter and easier to type than the classic scheme and also
allows branches with the same base to sort together.

Add a trivial test driver.

Add a repetition in the acceptance tests with the new naming scheme.

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/acceptance_tests.sh
$ ./testbed/arcyd/loop_test.sh

create r/ and arcyd-review/ branches and land in
$ ./testbed/arcyd/test_shell.sh