Add Probot stale config to avoid abandoned Issues/PRs

[dortegau]

Prerequisites

• Put an X between the brackets on this line if you have done all of the following:
  • Checked that your issue isn't already filled: https://github.com/issues?utf8=✓&q=is%3Aissue+user%3Aidealista
  • Checked that there is not already provided the described functionality

Description

It would be nice to automatically close staled issues. There are a nice GitHub Integration built with Probot that closes abandoned issues after a period of inactivity: https://github.com/apps/stale

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.