Added alphabetic sorting of groups.

[FlorianJunghanns]

This makes it possible to toggle between internal (currently creation time based) sorting of tab groups and alphabetic sorting in the UI.

[denschub]

else after a return statement is somewhat useless since it would never reach the code if the block above was true. You could simply omit the elses (which is was eslint suggests here). However, there is an even "nicer" (as in shorter) way of writing this sort code:

retGroups.sort((a, b) => {
  if (a.title == b.title) {
    return 0;
  }

  return a.title < b.title ? -1 : 1;
});

I tend to avoid ternary operation, but in such simple cases as deciding between 1 and -1, they are perfectly valid and easy to understand.

[denschub]

This is looking very good already, thank you so much for contributing! I've added a suggestion above. When done, could you please squash your commits into a single commit?

[denschub]

Merged, thank you very much!