Workaround problem of /latest.xml reporting non-existent old version

* In Cura.download.recipe:
    - Changed update_url to main software download page
	- Removed Process step using CuraUrlProvider.py (script left in-place for now)
	- Added Process steps to search download page HTML contents for current Mac version
	- Added Arguments to URLDownloader to combine update_url with matched regex for final download URL
Merge branch 'cura_fixup'

* Fix (temporary?) to scrape software download page rather than use /latest.xml which has been broken for weeks.