remove errors that never returns from server
match error messages that return from api
fix build error in WPYCreditCard due to change in
WPYErrors.
fix failing test in WPYTokenCreationTest due to 
change in WPYError
replace WPYInvalidNumber with WPYIncorrectNumber and
WPYInvalidExpiry with WPYIncorrectExpiry in 
WPYCreditCardTest
[bugfix] somehow removed error codes were replaced
by WPYIncorrectCvc. Replaced with proper error codes.
fix failing test cases due to change in error messages
add accept language parameter to WPYCommunicator

Allow setting accept-language header field.
Use error messages returned from api.
add new method that accepts acceptLanguage parameter
in WPYTokenizer.
add localization

- create WebpayiOSTokenizer.strings
- add japanese to WebpayiOSTokenizer.strings
create WPYDeviceSettings file
move preferredLanguage to WPYDeviceSettings
add isJapanese to WPYDeviceSettings
use isJapanese method from WPYDeviceSettings
change font and its size of field label depending
on preferred language on device.
[design] adjust line height & position 

- add line spacing for multi-line text
- adjust field label's left margin depending on 
os.(UITableView & Cell differs in size depending
on the ios version.)
[design]increase font size of field labels in ja

They looked too small.
[readme] update iOS version the library supports
[readme] refine explanation in overview

explain what it is when introduced.