Show "validation blocked" error in solidity files

[fvictorio]

When the project can't be compiled because no compatible solc version was found, we should show that as a file-level error in any solidity file. This would make it easier to figure out what's going on. Right now you have to notice a tiny tiny error symbol in the status bar.

For comparison, this is what eslint does when the file cannot be parsed: it shows that as an error in the first line and column.