Add bug report and feature request Issue Templates

[cshg]

Fixes #236

Type of change: Docs / Dev exp

Motivation

Have Issue Templates for Bugs and Features when open-sourcing UIKit.

Use new github feature of having several Issue Templates: https://blog.github.com/2018-05-02-issue-template-improvements/

Please check if the PR fulfills these requirements

• [x] Self-review: I am confident this is the simplest and clearest way to achieve the expected behaviour
• [x] There are no dependencies on other PRs or I have linked dependencies through Zenhub
• [x] The commit messages are clean and understandable

[janek]

sweet that those things exist, I didn't know that we can have 2 or 3 different templates. I think it's a great idea, but I might have some additional thoughts on how they should look like, once I get a bit further with demo app/coverage docs. Would you mind keeping this open for now?