python-uci: simplify Makefile by using sources from PyPI

As pyuci is now on PyPI, I was able to simplify Makefile
It means that we will download sources from PyPI.
- In this case, we don't need to have anymore PKG_SOURCE_* variables.
- Also, we don't need to update manually PKG_MIRROR_HASH by running
make package/foo/download and make package/foo/check

It would be enough to change just PKG_HASH and that's all.
PKG_HASH we can get on PyPI.

While at it:
- I added variable PKG_LICENSE_FILES and added source package.
- Fixed Section
- Improved Title to match title on PyPI