Remove need for OPENSLIDE and TURBOJPEG env variables

[jesper-molin]

I think it is complicated for an end user to get the right versions and set environment variables.

So I think we should find a reasonable way to ship openslide and turbojpeg binaries with the packaging, so they don't have to be installed manually and pointing them out using environment variables.

Dockerhub is one way to do it, but will still be unfamiliar for most people. I think the best solution would be pip dealt with it.

There are two options as I understand it. Either you ship it with the wheel package, I know shapely (https://github.com/Toblerity/Shapely) moved from not including the DLL to doing so. Or if the DLLs are too big or the license does not allow shipping the DLLs, there is also the possibility to have a script that fetches the DLL during install.

[sarthakpati]

I would also add that openslide is not particularly important/useful for pythonic environments. It would be better to use something like tiffslide in its stead.