refactor (plugin-webpack): extract methods from getDefines (#720)
refactor (plugin-webpack): extract methods from getDefines (#720)

* refactor(plugin-webpack): extract rendererEntryPoint method

* More descriptive parameter

* refactor(plugin-webpack): extract environment variable name generator method

* Ternary statements don't make sense if they're multi-line

* refactor(plugin-webpack): extract preload define value method

* fix(plugin-webpack): define process.env webpack entry vars

This is necessary when using Babel.

ISSUES CLOSED: #718

* Fix tslint warnings

electron-userland/electron-forge,electron-userland/electron-forge,electron-userland/electron-forge,electron-userland/electron-forge