Add compatibility of export/import JS scripts with Fx 68 ESR

[nohamelin]

• Services.search returns Javascript Promises now.
• Migrate from Components.utils.import to ChromeUtils.import
• Remove links to addons.mozilla.org
• More?

[joshcangit]

• Migrate from Components.utils.import to ChromeUtils.import

So far I can't find any documentation, changelogs or release notes referring to this. Only a commit on Mercurial.
MozReview-Commit-ID: BywABWvaiZf
Hopefully if there are further deprecations, there would be more information.

I might remove those forks when the changes are added.

• joshcangit/xseei.import.js
• joshcangit/xseei.export-all.js

[joshcangit]

• More?

Issue #7
Fix xseei.export-all.js file.