Add JSON specializations

[OneRandomGithubUser]

Add more presets to test new JSON capabilities of the mod. This tests office, commercial, mixed residential, and industrial specialization, separated by education level of workforce as well separating out gas stations, motels, and hotels from commercial areas. This also tests integration with official asset packs.

Possible future directions:

• Improve icons using education icons from Asset UI Manager (free Apache license) at https://github.com/qstar-inc/cities2-AssetUIManager/tree/master/Resources
• Add more support for default specializations for official asset packs.
• Add support for people to add their own custom specializations as separate Paradox Mods, using this mod as a dependency / required mod.
• Mod interplay: Asset UI Manager, Clean Industry Zones, Zoning By-Law Builder

Notes:

• If an asset pack is removed from Paradox Mods and there is currently a specialization that uses the asset pack, the mod errors. Errors are much worse if the asset pack is removed while the game is running (compared to if the asset pack is removed and then the game is restarted).
• Gas station, motel, and hotel specializations will sometimes spawn the wrong asset. Motels and hotels that get assigned the correct asset do not have functional room counts until the game is reloaded.

[DillonN]

Apologies, will be a week or so before I can take a closer look as I'm travelling without a PC that can run CSII. But thanks for the PR!