Xontrib-onepath

* Added debug mode e.g. `$XONTRIB_ONEPATH_DEBUG = True`
* Removed default action for `text/` type.
* Removed default action for `image/` type.
* Rewritten key part of code

xsh to py for compiled py.

Defaults changed to:

$XONTRIB_ONEPATH_ACTIONS['<DIR>'] = 'cd'

* Added check the actions by the order in the list
* Added `<XFILE>` type to catch executable files
* Added more examples

Added checking environment variable type.