Solve invalid pointer issue when loading skymodel

Investigate and solve issue with invalid pointer when loading skymodel. The problem turned out to be related to a mismatch between locally built python bindings for everybeam, and those that are installed through pip install lsmtool. This issue was fixed in this merge request for the rapthor-support repository in the build scripts for the different platforms.

For the Docker image, the problem turned out to be similar, but the mismatch was between python-casacore from the Ubuntu repository and the one on PyPI. The solution is to not install python bindings locally anymore.

Closes RAP-296