Prepare for VS2017 upgrade - workspace updates

This:

• Generates a VS solution for VS17
• Explicits the boost toolset chosen, leveraging ABI compatibility to avoid recompiling the library (for now).
• Likewise, reuses the Spidermonkey libraries. The SM60 upgrades does away with putting the toolset in the library name entirely.

Refs #5862

Differential Revision: https://code.wildfiregames.com/D3130