this carries through into the Targets.cmake file we install which in
turn means that the imported target for the consumer defines its include
directory. this removes the need to manually add the include dir
also updated the readme accordingly
Now it's the backend's responsibility to find LVM devices.
All LVM scanning code was moved into LvmDevice::scanSystemLVM helper,
so that it is very easy to plug LVM into backend.
LVM devices are now intentionally not detected in Dummy Backend.
Harald Sitter
Andrius Štikonas
Adriaan de Groot