[Gazebo9] More enhancement for Windows build

[seanyen]

• Installing the DLLs (shared libraries) into the bin folder by convention.
• Normalize the material paths into native paths so OGRE can discover them later. (Mixing the forward/backward slashes really confuses OGRE when looking up the resources.)
• Use the built-in tar.exe in Windows 10 (yes, there is a tar.exe with Windows) to unpack the downloaded asset. This could be a way to resolve this gap: [Gazebo9][Windows] ModelDatabase::GetModelPath implementation is incomplete on Windows build. #2611

[j-rivero]

Thanks Sean! changes looks good to me. Let me run another round of CI before merging. @osrf-jenkins run tests

[j-rivero]

The abi-checker killed the memory in CI, I'm not worried about. The Mac build is waiting #2809. Windows is happy. Let's wait a bit more for the linux ones.

[seanyen]

Thanks! And hope this can be forward-port to Gazebo11 if they also make sense there. :)