Register race condition fix

[omarzl]

This pr looks ugly but it is not.
It adds thread safety to the register to solve a race condition.

• I renamed SynchronizedResolver to SynchronizedContainer
• I created the protocols _Register and Register and I moved _register and register functions from Container to them.
• This allows me to be able to conform Register protocol in SynchronizedContainer and make it use the same NSLock object to make register calls thread safe.
• I modified Sources/SynchronizedContainer.Arguments.erb and ran script/gencode, there is where most of the changes come from.