iOS Simulator build refactor

Do not require iOS provision & cert, because the server does not need them anymore

Refactor the code to break the huge monolithic class into dedicated commands

Restructure the help of emulate command to make it platform-dependant
We might want to keep --[emulate]-- for the sake of consistency

--[emulate]--
Usage:
        $ appbuilder emulate <Platform>

You must run the emulate command with its target platform.

You can target the following platforms:
    android - Builds the specified project in the cloud and runs it in the native Android emulator.
    ios - Builds the specified project in the cloud and runs it in the native iOS Simulator.
    wp8 - Builds the specified project in the cloud and runs it in the native emulator from the Windows Phone 8.0 SDK.

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