Update to SMAPI 1.8, improve crossplatform compatibility, and fix config defaults

This pull request mainly...

• Updates to the latest SMAPI 1.8.
• Improves crossplatform compatibility.
• Moves the config.json defaults into the code, instead of shipping a default config.json. This fixes Linux/Mac compatibility (since colors are serialised differently from Windows), and ensures that deleting config.json resets the configuration instead of breaking it.
• Migrates to the mod build package to automate references (e.g. no longer need to specify the game path in the .csproj) and so the mod can be compiled on Linux/Mac/Windows without changes.
• Changes the manifest name to "Better Sprinklers" per our discussion.