Rework repo structure

[xmatthias]

• Move files to ftui directory
• Add pyproject.toml

use pip install build to install the build module, then run python -m build to create a source and wheel distribution (/dist directory).

Please Note that the pyproject.toml will still need some love when it comes to descriptions, tagging, ...

You can also install it locally pip install -e . - and you'll get a new binary freqtrade-ui - which can be used to run ftui.

[froggleston]

Thanks for the great additions - this looks and works great.