Trivial fixes

Fix spacing on an #import line in TSProtocolBufferWrapperTests.mm.
Fix file name in a comment in TextSecureViewController.m.
Remove unused #import in CountryViewController.m.
Add test for entering a US phone number

Also, make a trivial syntax change to VerificationViewController.m.

MONEYMONEY
Add test and fix to prevent empty country codes

This unit test verifies that the VerificationViewController resets the
countryCodeInput text and country value when the user does not enter a
country code in the input.  This behavior makes the previous
-(void)testEmptyCountryCodeCrash test obsolete.  An assert has been
added to prevent developers from repeating this error.

MONEYMONEY
Fix loss of country code after selecting country

When a user would select a country from the CountryViewController, if
the countryCodeInput became the firstResponder upon returning to the
VerificationViewController, the country code associated with the
selected country would be lost.  THis commit fixes and tests that
erroneous behavior.

MONEYMONEY
Merge pull request #87 from troyjfarrell/troyjfarrell-verificationviewcontroller

Add tests and clean up some country code UI