Consistent visibility of "Hide Republish Button" checkbox

[gamebits]

Updates code that determines whether Republication Tracker Tool's checkbox is shown in the post editor.

Changes proposed in this Pull Request:

The checkbox is currently visible only on alternating views of the post editor, with its settings getting lost in between. Closes #67 & #170.

How to test the changes in this Pull Request:

1. Create a post and check the "Hide the Republication sharing widget on this post?" box in the post settings.
2. Publish the post.
3. View the post on the frontend. Observe that the republication widget is not present.
4. Click "Edit Post".
5. Observe that the checkbox has been replaced with the notice "The Republication sharing widget on this post is programatically disabled through the hide_republication_widget filter. Read more about this filter." (This is a known issue: "Hide Republish Button" checkbox on posts shows "The Republication sharing widget on this post is programatically disabled..." message for filter only #67)
6. Click "Update".
7. View the post on the frontend. Observe that the republication widget is now present.
8. Switch to this branch. The checkbox is now always visible, and the setting is preserved between edits.

[adekbadek]

Thanks @gamebits !

[matticbot]

🎉 This PR is included in version 1.3.2-alpha.1 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀

[matticbot]

🎉 This PR is included in version 1.3.2 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀