[Suggestion] Allow decimal values when adding quantities in recipes

[l0f4r0]

It would be nice to allow the user to enter in decimal values when adding some items in recipe edition.

Expected Behavior

Recognize inputs like "0,80 cl vodka" or "0.30 cl gin".

Current Behavior

Parsing doesn't not recognize decimal values directly (the user needs to enter the value in fractional form like "1/2 cl vodka", not "0,50 cl vodka" nor "0.50 cl vodka").
NB: Edition afterwards works by modifying the "amount" field.

DEBUG info

Fractional form works:

DEBUG:   /tmp/.mount_GourmaWJJP1c/opt/python3.8/lib/python3.8/site-packages/gourmand/backends/db.py: 1889 ingredient_parser handed: 1/2 cl gin
DEBUG:   /tmp/.mount_GourmaWJJP1c/opt/python3.8/lib/python3.8/site-packages/gourmand/backends/db.py: 1934 ingredient_parser returning: {'amount': 0.5, 'unit': 'cl', 'item': 'gin', 'ingkey': 'gin'}

Decimal forms don't work:

DEBUG:   /tmp/.mount_GourmaWJJP1c/opt/python3.8/lib/python3.8/site-packages/gourmand/backends/db.py: 1889 ingredient_parser handed: 0,50 cl vermouth
DEBUG:   /tmp/.mount_GourmaWJJP1c/opt/python3.8/lib/python3.8/site-packages/gourmand/backends/db.py: 1937 Unable to parse 0,50 cl vermouth

DEBUG:   /tmp/.mount_GourmaWJJP1c/opt/python3.8/lib/python3.8/site-packages/gourmand/backends/db.py: 1889 ingredient_parser handed: 0.50 cl rhum
DEBUG:   /tmp/.mount_GourmaWJJP1c/opt/python3.8/lib/python3.8/site-packages/gourmand/backends/db.py: 1934 ingredient_parser returning: {'amount': 0.0, 'item': '.50 cl rhum', 'ingkey': '.50 cl rhum'}

Environment

Operating System: Linux Debian 10 64bits
Version or commit id: Gourmand-1.1.0rc2-x86_64.AppImage