Rename OS X to macOS in source code

[hbugdoll]

In my opinion all osx occurrences in source code should be renamed to macos.
The last OS X major version was realeased 7 years ago.

Example: realease asset file for macOS is still named mobilesdk-*.*.*.**-osx.zip

[cb1kenobi]

It's a good idea... a bit of work given we need backwards compatibility. Let's do it!

[caspahouzer]

@hbugdoll wanna contribute with some changes? Take a look at https://tidev.io/contribute