Use --webpack-use-polling to switch to fs polling mode on watch

[HyperBrain]

What did you implement:

Closes #215

How did you implement it:

The watch command now evaluates the --webpack-use-polling option with and without parameter
and turns on poll mode in Webpack's watch API.
Added documentation in the README to invoke local --watch and serverless-offline.

How can we verify it:

Use the switch (serverless invoke local --watch --webpack-use-polling) on a file system that does
not support events (Docker mounted volume).

Todos:

• Write tests
• Write documentation
• Fix linting errors
• Make sure code coverage hasn't dropped
• Provide verification config / commands / resources
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES
Is it a breaking change?: NO

[HyperBrain]

@barfet, can you check this PR and see if it solves the problem within Docker if you add the --webpack-use-polling switch?

[barfet]

@HyperBrain Sure, I'll check it tomorrow and will let you know. Thanks again for your efforts!

[barfet]

@HyperBrain Today I was able to test it in Docker with node --debug=0.0.0.0:5858 --nolazy node_modules/.bin/serverless offline --webpack-use-polling and it's working perfectly (debugging in VS code + recompilation on files changing in the host machine) thank you ones again!
When are you planning to release this feature? I'm very exited to use it in my project.

P.S.
Only one thing that I noticed is service folder was created in my out .build directory and compiled files was placed in it. Don't know if it's related to your commit, but my configuration wasn't changed from the last time and I have any configs to create this folder.

[HyperBrain]

@barfet Great to hear that it works 🎉 ! I will release it most likely end of this week (but merge it earlier to master).

The service folder is new with version 3.0.0 where the compiled service artifacts will be placed if you don't use individual packaging. I released the official 3.0.0 some days ago, so it might be that you previously used a 2.x version. So that's nothing to worry about 😄