umount a mounted USB drive before proceeding (or return to drive selection menu, if user does not approve umount) #192
Description
Is your feature request related to a problem? Please describe.
Sometimes the target USB drive happens to be mounted. This is especially annoying with "desktop environments", like Ubuntu, when each and every attached USB drive is automatically mounted. Flashing a new image onto a mounted drive is not good.
Describe the solution you'd like
It would be great, if caligula would check for mounted partitions on the target USB drive and ask for user's consent to umount them all. If user agrees to umount, then proceed with writing, otherwise return to the target drive selection menu.
It would also be great, to indicate in the target drive selection menu if some partitions of a USB drive are mounted.