Add timbre as a dependency for logging

The aim is to replace uses of log4j with timbre so that logging is
simpler to manage and acts in a way that users (that are not from JVM
land) understand better.

Link to project: https://github.com/ptaoussanis/timbre
Add conjure as a test dependency

This will be used for mocking and stubbing of functions. Rather than
explicitly re-binding everything, we can use conjure to provide easier
to read test stubs.
Remove clojure.tools.logging and replace with timbre

In most cases this is just a straight swap.

I've commented out some blocks that use a home-grown binding call to
point log4j's *logger-factory* at an internal atom vector. This could
be better pulled apart using conjure's mocking functions to point the
output wherever we want.