Fix: Push UI should not disappear when push is in progress

[dinhtungdu]

Description of the Change

• Add a background hack to prevent accident click when push is in progress.
• Keep UI visible when push is in progress.
• Fix watch task to make it work with gulp 4.

Alternate Designs

n/a

Benefits

• Better UX for pushing posts.

Possible Drawbacks

n/a

Verification Process

1. Set up and configure distributor, add at least 1 connection.
2. On the edit page, hover on the Distributor link of the admin bar.
3. See: the other parts of the page covered with a black overlay.
4. Choose a connection, click the Distribute button and quickly move the cursor outside the push UI.
5. See: the UI is still visible.
6. See: other parts of the edit page can't be clicked.

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

Closes #275

Changelog Entry

[dkotter]

While testing this, found one minor bug I left a comment about.

Overall I think this is better then what we have but I ran into on issue.

If I click to distribute something and then immediately move my cursor out of the dropdown, it stays open during and after the distribution, which is nice. But if I then move my cursor back to the overlay, it immediately closes, which is a little jarring.

[dinhtungdu]

Thank you @dkotter, I addressed all issues you mentioned, please take another look to this : )