[npm] Clean up package content

Currently npm packages contains folders like `.github`, and files like `.appveyor.yml` and `.travis.yml`. Those are probbably not useful in a package context, so should be excluded (if possible).

## Implementation Progress

### Platforms

- [x] cordova-android (https://github.com/apache/cordova-android/pull/958)
- [ ] cordova-browser
- [x] cordova-electron (https://github.com/apache/cordova-electron/pull/10)
- [x] cordova-ios (https://github.com/apache/cordova-ios/pull/863)
- [ ] cordova-osx
- [ ] cordova-test-platform
- [ ] cordova-windows

### Plugins

- [x] cordova-plugin-battery-status (https://github.com/apache/cordova-plugin-battery-status/pull/79)
- [x] cordova-plugin-camera (https://github.com/apache/cordova-plugin-camera/pull/575)
- [x] cordova-plugin-device (https://github.com/apache/cordova-plugin-device/pull/121)
- [x] cordova-plugin-dialogs (https://github.com/apache/cordova-plugin-dialogs/pull/135)
- [x] cordova-plugin-file (https://github.com/apache/cordova-plugin-file/pull/383)
- [x] cordova-plugin-geolocation (https://github.com/apache/cordova-plugin-geolocation/pull/192)
- [x] cordova-plugin-inappbrowser (https://github.com/apache/cordova-plugin-inappbrowser/pull/658)
- [x] cordova-plugin-media (https://github.com/apache/cordova-plugin-media/pull/275)
- [x] cordova-plugin-media-capture (https://github.com/apache/cordova-plugin-media-capture/pull/164)
- [x] cordova-plugin-network-information (https://github.com/apache/cordova-plugin-network-information/pull/103)
- [x] cordova-plugin-screen-orientation (https://github.com/apache/cordova-plugin-screen-orientation/pull/60)
- [x] cordova-plugin-splashscreen (https://github.com/apache/cordova-plugin-splashscreen/pull/251)
- [x] cordova-plugin-statusbar (https://github.com/apache/cordova-plugin-statusbar/pull/182)
- [x] cordova-plugin-vibration (https://github.com/apache/cordova-plugin-vibration/pull/85)
- [x] cordova-plugin-whitelist (https://github.com/apache/cordova-plugin-whitelist/pull/51)
- [x] cordova-plugin-wkwebview-engine (https://github.com/apache/cordova-plugin-wkwebview-engine/pull/137)

### Tooling

- [x] cordova-app-hello-world (https://github.com/apache/cordova-app-hello-world/pull/61)
- [ ] cordova-cli
- [ ] cordova-coho
- [x] cordova-common (https://github.com/apache/cordova-common/pull/104)
- [x] cordova-create (https://github.com/apache/cordova-create/pull/50)
- [ ] cordova-docs
- [x] cordova-fetch (https://github.com/apache/cordova-fetch/pull/74)
- [x] cordova-js
- [x] cordova-lib (https://github.com/apache/cordova-lib/pull/809)
- [ ] cordova-mobile-spec
- [x] cordova-node-xcode (https://github.com/apache/cordova-node-xcode/pull/96)
- [ ] cordova-paramedic
- [ ] cordova-plugin-test-framework
- [ ] cordova-plugman
- [ ] cordova-serve

_Excluded: `cordova-status`, `cordova`, and any unused, outdated, or deprecated repos_