Rename shared secret to client secret.

This is the terminology used by Canvas in the api docs,
so it makes more sense to be consistent this way.
Remove Pods/ from workspace.

This was getting real annoying.
Add Pods/ to .gitignore
Refactor keychain setters to avoid annoying logs

Previously, FXKeychain would print an annoying log for each property
message anytime you cleared the keychain and it was already empty.
Adjusted the setters so that you can now set the keychain property to
nil and it will remove it for you, but only if it's already set.
Refactor Keychain Properties

Add clientID and clientSecret so these will now save to the
keychain. Moved keychain category into its own file to clean
up CKIClient.
Rename a bunch of OAuth 2 related stuff.

Why? To be a bit more consistent with the names of properties the
Canvas API gives us. For example, what we were calling oauthToken
is returned to us as accessToken. There was no real reason to call
this oauthToken, and it is also unclear whether this should be
oauthToken or oAuthToken, etc. Kills two birds with one stone.
Remove styling code from CanvasKit

There is no reason for CanvasKit to be arbitrarily setting the color
of the UINavigationBar in the modal popover.
Merge remote-tracking branch 'instructure/CanvasKit/master'
Merge pull request #35 from jarsen/master

Wow. Much Pull. Very Request.