scan_dependency: support for ignoring optional dependencies, more doc
scan_dependency: support for ignoring optional dependencies, more
doc

Change-Id: I35c4d8034d375264eebd4c4e656c53a07602ae5a
Signed-off-by: Kunal Shroff <a3b6c3928a745b45becc135941c7c4a0f4436957@bnl.gov>

ControlSystemStudio/cs-studio,ControlSystemStudio/cs-studio,css-iter/cs-studio,ControlSystemStudio/cs-studio,ESSICS/cs-studio,css-iter/cs-studio,ESSICS/cs-studio,ESSICS/cs-studio,ESSICS/cs-studio,css-iter/cs-studio,ESSICS/cs-studio,ControlSystemStudio/cs-studio,css-iter/cs-studio,css-iter/cs-studio,ControlSystemStudio/cs-studio,css-iter/cs-studio,ESSICS/cs-studio,css-iter/cs-studio,ControlSystemStudio/cs-studio,ESSICS/cs-studio