Upgrade minimum Python version to 3.6
Detailed Description
Add maintainer script common/maintainer-scripts/upgrade_minimum_python_version to upgrade the minimum Python version required by LALSuite.
Upgrade minimum Python version from 3.5 to 3.6.
API Changes
Please tick one of the following options:
- 
These changes do not modify the API. 
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These changes do modify the API, and are backwards compatible. 
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These changes do modify the API, and are backwards incompatible. 
For examples of changes that do not modify the API and/or are considered backwards (in)compatible, please see the contributing guide.
Justification for Backwards Incompatible Changes
n/a
Review Status
n/a