allow to disable Node and Solidity compiler

[jpnovais]

Feature description

When applying the plug it automatically adds some tasks and runs npmInstall automatically. It would be good to allow to just generate the contract wrappers based on .abi files. This does not need NodeJS neither Solidity compiler.

[ogtega]

Even with the npm install and solidity compile step, is there a way to generate wrappers with only ABI files?

I tried following the source code to see where the plugin's outputs would go and just manually place my ABI files where they're expected, but I didn't have any luck.