fix: ensure dependencies are installed before spawning webpack

[Fatme]

If you delete node_modules of application and try to execute tns prepare or tns build, the following error is thrown:

Error: Cannot find module '<path-to-project>/node_modules/webpack/bin/webpack.js'
 at Function.Module._resolveFilename (internal/modules/cjs/loader.js:580:15)
    at Function.Module._load (internal/modules/cjs/loader.js:506:25)
    at Function.Module.runMain (internal/modules/cjs/loader.js:741:12)
    at startup (internal/bootstrap/node.js:285:19)
    at bootstrapNodeJSCore (internal/bootstrap/node.js:739:3)
Executing webpack failed with exit code 1.

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What is the current behavior?

What is the new behavior?

Fixes/Implements/Closes #[Issue Number].

[rosen-vladimirov]

But is this the correct place? Is this a service in this case or controller?

[Fatme]

It should be controller - I'll handle this in a separate PR.