Unify the *deployqt tools into a host tool in qtbase

We should unify the following deployment tools into a new tool called deployqt:

• androiddeployqt
• macdeployqt
• nacldeployqt
• windeployqt

deployqt would have a --platform option which would indicate the platform for which the application is being deployed. Appropriate options would be provided for platform-specific functionality, reusing arguments across platorms where appropriate. deployqt would be a host tool living in qtbase.

The old tools would remain, but as stubs that would construct an equivalent argument list for [android|mac|nacl|win]deployqt from the deployqt argument list, and simply exec deployqt. They would also print a warning announcing their deprecation.

At first, the implementations would be almost entirely distinct, and this initial work is primarily for changing the user-facing command line interface. Eventually, it would be nice to properly abstract a "dependency extraction and deployment API" from the various backends which could possibly be re-used elsewhere, as well as reading PE/Mach-O/ELF metadata directly rather than parsing the output of tools like otool.