Adding metadata save on each compile

[edisinovcic]

On each compile save metadata.json file to artifacts.

[yann300]

This will help fixing #72 .
Basically sourcify won't need to store the metadata in its plugin, but the metadata will be store in remix directly.
FYI we already store an artifact file (JSON) which contain another information (bytecode,...), in this PR we are saving exactly what the compiler outputs.
this also means that now we store 2 files for each compiled contracts.

• < contractname >.json : contains gas estimation, bytecode, sourcemaps,...
• < contractname >_metadata.json the actual compiler metada output

[edisinovcic]

If everything is good @ioedeveloper @yann300 feel free to merge.

[yann300]

@edisinovcic ok, could you just remove the remaining console.log

[edisinovcic]

@yann300 solved.