Revert "Merge pull request #46 from zendesk/nherment/RADAR-235_refactor_presence"

This reverts commit 53224754da3e9f8e4268df8a8e16b99e53796c9e, reversing
changes made to 2fca2907f58a838d6551cf2c5e70494380375d01.

Conflicts:
	tests/client.presence.test.js
Merge pull request #53 from zendesk/vanchi/revert_presence_refactor

Revert "Merge pull request #46 from zendesk/nherment/RADAR-235_refactor_...