RFR: jpkg contents/show commands

[Chris Hegarty]

This change adds two new commands to the packaging tool. 'jpkg show' and 
'jpkg contents', which came up on this list a few weeks ago.

http://cr.openjdk.java.net/~chegar/jigsaw/jpkg_contents.00/webrev/

Also, included is various cleanup and restructuring, especially to 
ModuleFile, to put in place a structure to more easily support new 
compression algorithms. Specifically LZMA. I have a prototype from last 
year I need to rebase.

For now, 'contents' and 'show' are only added jpkg, but I could see that 
these may be useful before installing a module into the module library, 
so could be applicable to the jmod command also? Or just jmod?

If these new commands are to stay in jpkg long term we should probably 
change the command that builds the jmod/deb files to create/build, so 
'jpkg create ... jmod'.

Two specific implementation changes to draw attention to in the webrev:
  1) ModuleFile.java (L535 new  file). Resources were never being
     deflated in the module library. They are now.
  2) Sean,
     Can you verify the changes to changes to Singer and
     ModuleFile.SignatureSection? All jigsaw signing related tests pass.

-Chris.