combine fwget and fwfind into fw2json

[holderg]

If flags for group/project/subject/session/acquisition try all flags as for fw.find
else
try for uuid
else try for fw.get/fw.find

[holderg]

fw2json takes arguments for fw.get as well as fw path sets.
It doesn't do fw.find in part because it doesn't know what type of container to look for.