Review request JDK-8015912: jdeps support to output in dot file format

[Mandy Chung]

This adds jdeps --format=dot option to print the output in dot-style 
format that can be taken to generate a dependency graph.

Webrev at:
http://cr.openjdk.java.net/~mchung/jdk8/webrevs/8015912/webrev.00/

This also extends --verbose option to take an optional argument ("class" 
and "package") to replace the --verbose-level option and cleans up 
PlatformClassPath to use java.nio.file.

thanks
Mandy