Feature: fnc new should let user select package manager

[seppwc]

from: #3

fnc new should ask whether user wishes to use yarn or npm and change project files accordingly

1. give user either/or option of NPM or Yarn
2. when selection is given, package.json scripts need to changes to the correct version (eg. "npm run start" or "yarn start")

Test:

fnc new [directory]
// project should ask "Initialise with which package manger?"
// options: "npm", "yarn"
cd [directory]
npm/yarn install //should install dependancies
npm run / yarn start //should start development server
// check package.json, scripts should use correct package manager