Add userInfo or other property to IndicatorInfo to support more situations

[gonghao]

Recently I need to add badge support for Tab, but I found the IndicatorInfo do not support property other than title, image and highlightedImage. It isn't flexible enough to customize the Tab, although I write the TabCell to do so, I have to use the image property to do some hack.

Maybe we should add the extension ability for IndicatorInfo to have a more flexible use.

If it was OK, I very appreciate making a pull request about this.

Thank you.

[santiagofm]

Hey @gonghao, we agree with you and had some discussion based on #368 (comment) about what to do- making IndicatorInfo a protocol for example- but it may require some heavy restructuring and decided to add the task to our backlog and work on it after we reduce the issue count.
That said, feel free to open a PR with whatever you have in mind.

Cheers