build: separate development dependencies

[uniqueg]

Description

• Add requirements_dev.txt for dependencies that are only required for testing/developing FOCA
• Move dependencies required for packaging to setup() option setup_requires in setup.py
• Use requirements.txt only for dependencies that are required for running FOCA

Fixes #95

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have not reduced the existing code coverage