Add subpath flag for nested destination

[Oren Farhi]

user should be able to add another sub path for the destination.
if this dogen task has been defined in a dogen.js:

dogen.task('endpoint', 'src/server/api');

running this cli in terminal/cmd:

gulp dogen --endpoint guitars --path common/others/  

then, the path should be concatenated with the destination that was defined in the 'endpoint's task method, so the template's new files will be located in:
src/server/api/common/others