Add option to clean up /var/local/oab/src folder #95

Hi,

Perhaps after the packages were build, the src folder is no longer needed?
Looking at space usage, it seems to occupy the most space:

$ du -d 1 -h /var/local/oab
4.0K    /var/local/oab/gpg
328K    /var/local/oab/srcs
987M    /var/local/oab/src    <--- lots of wasted SSD space
107M    /var/local/oab/deb
138M    /var/local/oab/pkg
1.3G    /var/local/oab

If cleaning up this folder is acceptable, can we have this feature (perhaps enabled by default?).