Fix 64-bit iOS unit tests

Under 64-bit iOS, the `BOOL` type has changed from `signed char` to `bool` but NSNumber did not get the memo. So [@NO objCType] (which is equivalent to [[NSNumber numberWithBool:NO] objCType]) returns "c" (_C_CHR) instead of "B" (_C_BOOL). OCMock uses this information to check that the mock return type is compatible with the expected return type. Using the OCMOCK_VALUE macro solves the problem since it explicitly encodes the `BOOL` type.
Update the App.net certificate

App.net recently updated their certificate, maybe because of the Heartbleed bug. Since the example app does certificate pinning it stopped working as the certificate did not match.
Update the App.net API base URL
Merge pull request #1987 from 0xced/update-adn-certificate

Update the App.net certificate
Merge pull request #1986 from 0xced/fix-64-bit-unit-tests

Fix 64-bit iOS unit tests
Perform KVO with a dedicated observer object (AFTaskProgressObserver)

This solves the problem of smashing `observeValueForKeyPath:ofObject:change:context:` with a category on UIProgressView.