Move unit tests to their own module

[crabmusket]

There should be a single Project Generator or CMake switch to enable unit tests across all submodules. The code should be excluded from the engine if tests are not enabled.

[Areloch]

That's a good idea.

I can update the TS unit test to abide this, and I'll look at bringing the existing tests to bear with it as well.

Should be pretty easy right now, as they're self contained in their own little bubble ;)

[crabmusket]

Yeah, and I do like that they have their own little ghetto :P. The problem is, if you want to add/remove a module that has unit tests, I don't want you to have to move source files into/out of the tests directory - the tests should be contained in the director(y|ies) added by the plugin. So overall I think a #define is probably our best bet, and just wrap all the unit test files in it. Unless someone else has a better solution.

[crabmusket]

Torque 2D simply uses the TORQUE_SHIPPING flag to exclude tests. I find this acceptable, and it's probably best practise to try and align T2D and T3D somewhat. They also use googletest which I like the idea of. I've had brief experience with it before. Making a new ticket for discussion.

[crabmusket]

As part of #706, I've added a flag TORQUE_TESTS_ENABLED which controls the unit tests, and is set by including a module called 'testing'. Just seems like a good idea to only include the 30,000 line google test library if users really want it. If they're not going to bother with tests, then ignore it.

[LuisAntonRebollo]

Good idea to add the flag.

I'll try this weekend.