[docs] Updated OpenWRT version to 19.07 in README
[fix] Run make clean before new compilations
This fixes issues during compilation for different architectures.
[change] Removed obsolete luci-openwisp #13
Closes #13
[change] upload_firmware.py: allow adding new images to existing build
[change] Updated to support latest openwisp-config (without SSL variants)
[change] Extract image builders right after compilation
Necessary due to the fact that now make clean is run
after each round.
[change] Cleanup and create generator dir before find scripts are executed