Make XHProf easier for me to use with other users

Summary: Ideally there should be a "send epriestley this profile" button but this is a reasonable step forward. Add a "download .xhprof profile" button to profiles, since walking through these things remotely is pretty awkward. Also expand "Excl" and "Incl" acronyms.

Test Plan: Clicked download button.

Reviewers: csilvers, btrahan, vrana

Reviewed By: csilvers

CC: aran

Differential Revision: https://secure.phabricator.com/D2523