Bug 1027717 - Use package manager in calendar r=millermedeiros

uhm, caldav and ical should follow semver if possible. - but I'm OK with simply using master for now. 

was also wondering if we should use semver ranges for all dependencies, but at the same time I kinda like *shrinkwrap* since it avoids errors caused by different dependency versions (those are really hard to catch and leads to *"but works on my computer"* scenarios).

 > "... but It works on my laptop."
 > "Back-up your e-mail, your laptop is going to production."