Add support for netinstall

[merajmasuk]

Problem

Already mentioned in issue #870 that in some particular scenario installer freezes and stuck in a loop while adding CDROM to apt sources. Thus blocking the whole installation process. In my opinion, there should be alternative options such as net based install so that user can choose that if the live install fails.

Proposal

Have a checkbox to turn allow/disable download sources using network using installation.

Preconditions:

• At least one form of internet connection must be active.

Prior Art (Optional)

No response