Remove `dwall` since the program is not up to date with the API.
Add comments and improve `sshrnotify`.
Dependencies management improvements.

* Actions returns a list of commands to execute instead of a single command.
* Add a `clean` action that will remove any folder not specified in the
  dependencies structure.
* Add a `all` action that will run `clean`, `install` and `update`.
* Improve the `update` Git action to reset the repository and enforce the
  remote URL before pulling.
Improvements on dependencies management script.

* Now support a cache file for currently installed dependencies. If the
  dependency type or any parameter is modified, the old dependency will
  be removed.
* Add a JSON cache file as fallback for YAML file; if the YAML extension
  is not installed and a JSON file is present, the JSON file will be
  loaded (only if the YAML is not more recent).