Version pinning too rigid in setup.py files

[mbyrnepr2]

Describe the bug
The fix for this issue should resolve the behaviour we are seeing in this comment..

Currently resc-backend, vcs-scanner and vcs-scraper have pinned to exact version most of their 3rd-party dependencies.
This can cause conflicts when pip tries to resolve them during installation and my environment also requires packages which have different versions of these same packages.

If certain dependencies are undesirable for some reason then they can be excluded as an exception as in the following example, but it's easier for the libraries to be installed successfully if the version requirements are not so strict. Perhaps also a comment would be good to add in order to provide a rationale to future developers when this occurs.
Django>=1.4.2,!=1.5.,!=1.6.

To Reproduce
Create a requirements.txt and have two requirements: resc-backend and celery >5.3.1

ERROR: Cannot install -r .\requirements.txt (line 8) and celery>5.3.1 because these package versions have conflicting dependencies.

The conflict is caused by:
    The user requested celery>5.3.1
    resc-backend 2.0.0 depends on celery==5.3.1

To fix this you could try to:
1. loosen the range of package versions you've specified
2. remove package versions to allow pip attempt to solve the dependency conflict

ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/topics/dependency-resolution/#dealing-with-dependency-conflicts

Expected behavior
Allow a range with an optional lower bound. Exclude any versions which are problematic for security reasons, for example.
Otherwise, instead of celery==2.0.0 -> celery

Additional context
Stack overflow.
https://caremad.io/posts/2013/07/setup-vs-requirement/