Deprecate usage of `electron-packager`

[SimulatedGREG]

As electron-vue has grown over the past year, it has become apparent that the advanced usage of webpack, asset handling, and dependency management has become too troublesome to handle with the simple setup of electron-packager.

electron-builder on the other hand is able to handle all of the above features and go beyond those if needed. In the end, the benefits here just don't compare to electron-packager like they once did in the past.

Related: #292

Update

Currently npm@5.3.0 has an issue related to pruning dependencies, which can result in missing modules for builds. The use of the yarn package manager is very recommended.

Related:
npm/npm#17781
#338

[develar]

#310 Electron-webpack can be used with any package tool, but only electron-builder allows you to copy files on the fly and construct any dist out as you want. Because of that, dist out is simplified.

In the future electron builder will use webpack in memory fs to build project directly to asar archive.