Use custom icons for each browser

[wmorland]

Currently we just use generic icons. By using the same icons as used in by the App (for example in the doc) it will be easier for users to quickly pick a browser at a glance.

We will need to either store or fetch the icons and then set them when we add items:

alfred-py3-default-browser/defaultbrowser.py

Lines 45 to 50 in c8ea635

	if browser == current_default:
	wf.add_item(title=browser, icon=workflow.ICON_FAVOURITE, valid=False)
	else:
	wf.add_item(
	title=browser, icon=workflow.ICON_WEB, valid=True, arg=browser
	)

For reference @stuartcryan does this by having a folder with different images already available https://github.com/stuartcryan/defaultbrowser-alfred-workflow/tree/master/workflow/images