Remove pull requests from issue list

[cloudhx]

According to GitHub API documentation:

GitHub's REST API v3 considers every pull request an issue, but not every issue is a pull request. For this reason, "Issues" endpoints may return both issues and pull requests in the response. You can identify pull requests by the pull_request key.
Be aware that the id of a pull request returned from "Issues" endpoints will be an issue id. To find out the pull request id, use the "List pull requests" endpoint.

Considering the below requirements refer in particular to the GitHub Issues feature, the pull requests should be filtered out from the issues returned from API.

As a bare minimum, the application should support:

• Signing into GitHub (e.g. using your Personal Access Token).
• Listing issues assigned to you.
• Closing issues one at a time.

[cloudhx]

This change is shelved.