Download progress on main loop/thread.

[Vingian]

Description

Schedule the download progress update on the main loop/thread.

Fix #3578, fix #3553 and fix #3629

Type of change

• 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)
• This change requires a documentation update

[github-actions]

Pylint result on modfied files:

************* Module bottles.frontend.widgets.component
bottles/frontend/widgets/component.py:97:45: W0511: TODO: unimplemented (fixme)
bottles/frontend/widgets/component.py:21:0: E0611: No name 'Adw' in module 'gi.repository' (no-name-in-module)
bottles/frontend/widgets/component.py:90:35: W0613: Unused argument 'error' (unused-argument)
bottles/frontend/widgets/component.py:88:23: W0613: Unused argument 'widget' (unused-argument)
bottles/frontend/widgets/component.py:110:27: W0613: Unused argument 'error' (unused-argument)
bottles/frontend/widgets/component.py:108:24: W0613: Unused argument 'widget' (unused-argument)
bottles/frontend/widgets/component.py:126:25: W0613: Unused argument 'widget' (unused-argument)
bottles/frontend/widgets/component.py:134:4: R1710: Either all return statements in a function should return an expression, or none of them should. (inconsistent-return-statements)
bottles/frontend/widgets/component.py:182:0: R0903: Too few public methods (0/2) (too-few-public-methods)

[EmoonX]

Minor and meta thingie, but I think GitHub missed the second issue here: