Only copy the necessary files from the source python folder to the build folder

[hakonhagland]

Depends on #3040 which should be merged first.

For background information, see: https://github.com/OPM/opm-simulators/pull/3918#pullrequestreview-997949357

Instead of copying the whole python folder to the build folder at build time, only copy the files that are considered to be necessary. This means the opm, cxx, tests, and examples directories and the install.py script.

[hakonhagland]

jenkins build this opm-simulators=3938 please

[blattms]

jenkins build this please

[blattms]

Mmh, this has been hanging for some time and we might want to get this into the release mabye. @hakonhagland would that make sense and do you think you can find time to rebase it on top of current master to get rid off the conflicts?