Add retry to failed actions

[douglasdcm]

The 'at' command in Application class may be configured to retry the 'do' methods when they fail. It can be accomplished with a naive and procedural loop or by decorators and singleton classes to hold the number of retries on each iteration. The retry should be disabled by default and the user can enable it by environment variables put in .env file. At least tow variables are need. One to enabled or disabled the feature and other to set the maximum number of retries per actions