Updating tycho-jnlp-plugin for JAR files security features, required from jdk7u25

Add -digestalg for jarsigner, default algorithm changed for jarsigner in jdk7. 
Add options for JAR file manifest attributes for security (Permissions, Codebase, etc... ) and delete precedent signatures. 
Add possibility to sign the JNLP file into the main jar file. A JNLP template file can be used.