Suppress some diagnostics

[just-boris]

I get the following output at the end of webpack build

ERROR in [default]
File 'src/layouts/application/AppLayout.hbs' has unsupported extension. The only supported extensions are '.ts', '.tsx', '.d.ts'.

ERROR in [default] src/app.ts:2:22
Cannot find module './layouts/application/AppLayout.ts'.

ERROR in [default] src/index.ts:3:16
Cannot find module './app.ts'.

ERROR in [default] src/layouts/application/AppLayout.ts:4:26
Cannot find module './AppLayout.hbs'.

All files actually have been successfully imported by webpack, but during typescript compilation it doesn't know about it and report errors.

Now it always written in console output and distracts from real errors. It would be nice to have ability to disable errors by its code.

These errors has following codes
TS2307 - Cannot find module
TS6054 -File has unsupported extension.

[just-boris]

Also, found that breaks ExtractTextPlugin.
It refuses to extract content if it has erorrs. See this commit.

Because errors from comment above is not actually an error, it should not be reported to webpack and break other plugins

[s-panferov]

I believe that now it can be achieved by allowNonTsExtensions tsconfig option.