Use antd splitter (#9)

See https://ant.design/components/splitter

Mostly NFC, yet it adds an ability to spawn new IR window not
only verticaly (default) but also horizontaly.

Removed Collapse button for the left panel - with the splitter
it can be collapsed much better.

Please run npm install one more time, as this PR brings new
dependency in the package.json

Special thanks to @clima365 for the pointer on antd!

TODO:
- add ability to have more than 1 Source Code
- Control IR windows smarter

Author: MrSidims