Make adding cake.config to Solution Items opt-in (or remove this feature)

[augustoproiete]

Currently if there's a cake.config present in the root folder of the repo, the VS extension modifies the Solution file and adds the cake.config to a solution folder called "Solution Items" (hard-coded).

The extension should not make changes to files unless the user explicit invokes an action.

I suggest making this feature opt-in via configuration, or completely remove the feature if easier.