Migrate issue tracker to GitHub

[magreenblatt]

After considering available options we have decided to migrate [1] the JCEF issue tracker from BitBucket to GitHub.

Migrating issues to GitHub allows access to some nice features that don't currently exist on BitBucket:

• Task lists
• Converting between issues and discussions
• Many new ways to create issues (from code lines, comments, etc)
• Finding/grouping issues by labels

[1] Migration is being accomplished using this tool (with PRs 126, 139, 140, 141, 142, 144 applied).

Related forum thread: https://magpcss.org/ceforum/viewtopic.php?f=6&t=19387

[magreenblatt]

All Bitbucket issues have been migrated and the GitHub issue tracker is now writable.