Support forceExclude to exclude dependencies

[HyperBrain]

What did you implement:

Closes #247

How did you implement it:

The configuration now allows for a forceExclude array besides the forceInclude array. All modules specified will be forcefully excluded, even if they appear as production dependencies. If the excluded dependency includes a peer dependency, this has to be excluded manually because the peer is still required, even if the excluded dependency is drawn from somewhere else.

Sample:

#serverless.yml
custom:
  webpackIncludeModules:
    forceInclude:
      - module1
    forceExclude:
      - module2

The precedence is exclude -> include, i.e. if a module appears in include as well as in exclude, it will be excluded (exclude wins).

How can we verify it:

Just use a configuration as in the sample above, do a serverless package and check the zip files created in .serverless.

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