Merge some stalled/closed PRs in Palantir

[ccordoba12]

@steff456, I'd like you to merge here (but preserving authorship) the following PR's from the Palantir repo:

• setup.py: exclude all test packages palantir/python-language-server#443 (low)
• Pass document path to plugin settings palantir/python-language-server#418 (important)
• Allow to use custom python interpreter [fixes #339] palantir/python-language-server#401 (critical)
• Add Lint Trigger palantir/python-language-server#393 (low)
• Add mypy support using daemon palantir/python-language-server#392 (there's already a plugin for this. Check what works better).
• Add pylint support. palantir/python-language-server#385 or Add pylint support palantir/python-language-server#384 (low / only one of the two, 384 seems better)
• Added pyls.extraSysPath. Fixes #381 palantir/python-language-server#382 (critical for our additions to PYTHONPATH. We need to do the same for Rope).
• Fix parent process being killed on Windows when checking if it's alive palantir/python-language-server#445 (critical on Windows).

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Notes:

1. Please restore first the race between Rope and Jedi. After that we'll release the first version of our fork and then you'll proceed with this work.
2. Next to each PR I mention how important I think it is. So please merge them in that order (critical -> important -> low).