Add support for native Plover commands

[jladdjr]

Currently, in order to invoke plover-ninja commands, you need to write out a phrase, like "I am ready to practice" or "show stats".

In addition to this behavior, there should also be a Plover command for each plover-ninja command.

Acceptance Criteria:

• Plover Commands for each of the commands currently supported by plover-ninja
• Unit tests for the new behavior
• Documentation on how to configure and use the Plover commands supported by plover-ninja
• plover-ninja commands must be tested on Linux and Mac, and if possible tested on Windows, too
• Create a new release with release notes that document the support added for this feature
• Regression testing to ensure that upgrading to newest release can be done successfully
• Confirm that new release can be used for both fresh installs and upgrades using the Plover plugin manager