Dragonfly's typeable and keyboard related files have been heavily
modified to do this:

- The *dragonfly/actions/keyboard.py* file is now a sub package
  instead.
- The Windows Keyboard class has been moved to a new file:
  *dragonfly/actions/keyboard/_win32.py*.
- KeySymbols classes for supported platforms have been defined that
  map common key names to platform-specific key symbols, e.g.
  "LSUPER" -> "win32con.VK_LWIN".
- "from dragonfly import Keyboard, Typeable" (or equivalent) will
  now import classes for the current platform.

Python 2.7 raises errors in 'except' blocks as expected,
but Python 3 doesn't. This commit changes Key to check if the
typeable exists using 'get()' instead of catching a KeyError.

This is possible now that the Key and Text actions are working.
The system clipboard is used through the pyperclip Clipboard class
on Mac OS and X11.

This commit also fixes a bug where None can be passed to
pyperclip.copy() and raise an error.

The "xev" program is used to capture key presses, so it must be
installed. This script is not a unit test file.

- Press a few more keys twice: F11, Super_L and Super_R.
- Decode lines from 'xev' before using them.
- Remove the "npsep" key because it sometimes doesn't work.

- Make each mocked action refer to a class instead.
- Replace mock_dyn_str_action with a mocked Mouse class, as that
  action is the only DynStrActionBase sub-class left that isn't
  implemented for other platforms.