updated PSPDFKit to v4.0.3 and extracted the plugin demo app into separate folder;
fixed pspdfkit.js path in plugin.xml
added PSPDFKit's Cordova plugin to PSPDFKit-Cordova-Demo app
updated plugin source code for the PSPDFKit v4.0.3
Merge pull request #9 from PSPDFKit/v4-restructure

updated PSPDFKit to v4.0.3; Separated plugin and the demo app;