[UPD] Enforce C++ version and improve 'setup.py' flexibility

Context

1. C++-14

Fixes aidge_core#225 (closed) for aidge_backend_opencv. The same update must be done on every module.

2. Python module compilation

Also increase 'setup.py' compilation option flexibility using environment variables. Made to work with aidge!97 (merged)

changed milestone to %aidge v0.5.0

added Compilation ⚙ label

assigned to @pineapple

added 5 commits

• ec8eb98b...74dceb66 - 2 commits from branch dev
• e61de7a6 - Enforce C++-14 in 'CMakeLists.txt'
• 1e6a8f20 - Change Python minimum version 3.7 -> 3.8
• fe276c4b - UPD: 'setup.py' to access compilation options from environment variables set by 'setup.sh'

Compare with previous version

added 4 commits

• f0673207 - 1 commit from branch dev
• c27494ef - Enforce C++-14 in 'CMakeLists.txt'
• fa8848ac - Change Python minimum version 3.7 -> 3.8
• 39931330 - UPD: 'setup.py' to access compilation options from environment variables set by 'setup.sh'

Compare with previous version

enabled an automatic merge when all merge checks for 39931330 pass

mentioned in commit dfa11c3a

merged