ui/Tooltip - basic implementation of tooltip overlay

[Goondrious]

I did a basic implementation for #224 and tried to keep it flexible, since there hadn't been a design discussion yet. I quickly looked at some existing packages, but they didn't seem compatible with the Hoverable/Button implementation.

I'm pretty new to typescript, react native and this project, so I'd be happy to refactor to conform to any standards that I missed.

Immediate TODOs or improvements would be:

• [] more configurable style related props (e.g. color of background & text)
• [] stay on screen
• [] switch the usage from supplying a ref of the desired component to composition with built-in hover/touch/arbitrary trigger

[CLAassistant]

All committers have signed the CLA.

[andymatuschak]

(I'm out of town this week but will get back to you next week—thank you!)

[Goondrious]

No worries @andymatuschak , thanks for the response.

My TypeScript experience has just been in passing, though now I've used it more in personal projects. I feel bad that you went through and did some of the basic tidying up, which I had purposefully left assuming that much would change through any design discussion. Sorry if it caused unnecessary effort/stress on your part. Thank you! I'll review your changes, as I'm sure it'll be a good learning experience. I was actually anticipating a blanket, "please fix type/lint errors".

Hoping to go through more specific comments later this week.

[Goondrious]

Apologies, I got caught up with some other work and holidays. Hopefully back to this soon.

[Goondrious]

@andymatuschak base checks pass. Can sort out styling, configurability and anything else. I'm also around for the next few weeks if there are other tasks you'd like help with.