Implement PatternLayout

[UnderMybrella]

While this currently works fully, it's not necessarily perfect, so let me know what needs to be changed.

This change creates a PatternLayout for Sawtooth configuration that accepts a string such as "%logger: %msg" and tokenises it, allowing custom output.

Each token accepts a set of modifiers, passed via braces "%epoch{ms}"; it is the responsibility of the PatternComponent to parse these modifiers and determine how to process them.

Supersedes #4