* Change LICENSE to LGPLv3

As agreed between @glotaran/pyglotaran_creators on Feb 8th 2021 the LICENSE shall be changed to LGPLv3 in preparation for the v0.3.0 release and going forward.

* Updated setup.py to match change of licenses

Changed references to GPLv3 to LGPLv3.
Also updated the development status to 3 - Alpha in preparation for the 0.3.0 release.