Don't download the Python indexer during compilation

[matejak]

Hello, I am trying to help with the Fedora package of Sourcetrail, and I have noticed that when one wants to compile it with Python support, the build attempts to download the compiled indexer. This is unfortunate, as downloading compiled archive during compilation doesn't make much sense, but more importantly - wouldn't it be better to optionally compile support for Python indexing at compile-time and switch the actual indexing feature on or off at run-time depending on whether the indexer is available?