scanlibs.py: support reading dependencies file, custom plot options
scanlibs.py: support reading dependencies file, custom plot options

Due to reading from dependencies file support, the pyelftools library
(https://github.com/eliben/pyelftools) is optional. Due to optional
plotting support, the networkx and pygraphviz libraries are optional.

The '-plot' option was renamed to '--plot' due to argparse usage.

H1ghT0p/make-gapps-zip,Lekensteyn/make-gapps-zip,Lekensteyn/make-gapps-zip,H1ghT0p/make-gapps-zip