Extract some "mixin" shared contexts from the hbase shared context.

It was getting unweildy.  Also make some methods private & drop use of
(now no-op) :test_classpath.
askari/schema/application aliases the v0 application class.

This protects disinterested code from versioning changes.  A schema
client still needs to be aware of format versioning, but they should
examine the `format` attribute of the application instance to do so.
A tool can create and perform plans (Enumerables) of Actions.

An action is a proc with a descripton.
Visitation implements half of the visitor pattern.

Tool (and mixers) will implement the other half.