Remove -[BTRTextField updateState] (#56).

Change-Id: I66d9be714cf90422fc182ebec5e7487c4ea12ecd
Remove -[BTRHandleStateChange].

- As the method no longer does anything as of 87e29bf8f3cd25f0c676149c7eb9138d971691d6.

Change-Id: I06a19d4dd2806b8fad9b84cbe06f00e1537d2174
Remove -[BTRTextField updateStateWithOld:new:].

- As it only performed an assignment as of 738a07e619d37713269fd87c7fb161d5fdc780d3.

Change-Id: I04682dc4108f8a77efd32c727c09a5e67334e8a5
Remove import of unused header.
Add BTRSecureTextField to text field demo app.

- Xcode first tried to upgrade the XIB to 5.1 and up only (silently of
course). I’ve set the IB compatibility setting to Xcode 4.6.
- I’d argue that it should be raised to 5.0 or 5.1 as the XIB becomes a
whole lot better then.
Refactor out the BTRTextField API into protocol.

- This is so that it’ll be easier to keep BTRTextField and
BTRSecureTextField in sync.
Sync BTRSecureTextField implementation with BTRTextField.

- They were quite a lot out of sync.
- Both now use a shared protocol to define the shared public API. This
should hopefully make it somewhat easier to spot if this happens in the
future.
Change BTRTextFieldProtocol.h file to be public.
Remove old comment on BTRTextField.
Merge remote-tracking branch 'upstream/master' into purge-update-state

Conflicts:
	Butter/BTRSecureTextField.m
Change name of common init function for secure text field.

- So that the naming matches that used in the `BTRTextField`
implementation.
- Should have no actual consequences for the code.
Merge pull request #57 from rastersize/purge-update-state

Remove a few methods that don’t do anything anymore