Change signjar task to apply/exec jarsigner with custom args

The ant signjar task doesn't support -storepass:file.
Note this no longer preserves the original file modification time.
Replace jarsign.storepass property with jarsign.storepassfile

Added default password file lib/keystore.passwd
Replace genkey task with exec keytool -genkey

Need to use -storepass:file
Add jarsigner timestamping
Set default timestamping authority to http://time.certum.pl