Task: Abstract packager to a common interface so that other packagers can be used

[HyperBrain]

This is a Feature Proposal

Description

The packager (currently NPM) should be extracted into a separate internal module with a generic interface. This is necessary to enable support for other packagers like yarn.

As soon as this has been done, Yarn support can be implemented.

Similar or dependent issue(s):

• Support optional use of Yarn for packaging (instead of NPM) #286

Additional Data

• Serverless-Webpack Version you're using:
• Webpack version you're using:
• Serverless Framework Version you're using:
• Operating System:
• Stack Trace (if available):