rename this tip to be less confusing

Using props to initialize state is completely fine; the issue is using state as a "cache" for values calculated based off of props. This title makes it more clear.
fixing capitalization
Upgrade populist dependency to v0.1.6.

This reduces the time taken by `grunt populist:test` from 7s to 550ms,
which should make @spicyj especially happy.

Relevant commits from the `populist` and `ast-types` repositories:
https://github.com/benjamn/populist/commit/9863ad16c0753f714fdb83007515637511c346d6
https://github.com/benjamn/ast-types/commit/dabef2a4ac48ebdb5c76baf1fb94f4997b6484ac
Merge pull request #672 from benjamn/upgrade-populist

Upgrade populist dependency to v0.1.6.
adding note about initializing state w/ props
changes as requested
one liner
A new helper for tests: createHierarchyRenderer

We aren't using this in any of the React tests, but we've found it
useful testing product code.
Tutorial template markup needs a reference to jquery for the ajax calls
from step 13 onwards.
Merge pull request #674 from squidsoup/tutorial-jquery-src

Documentation (minor): template missing jquery reference
Merge pull request #650 from jaredly/patch-1

rename this tip to be less confusing