added pdfView and setup demo to view PDFs in assets folder
Merge remote-tracking branch 'origin/master'

Conflicts:
	.idea/libraries/support_v4_19_1_0.xml
	app/app.iml
	app/build.gradle
	build/intermediates/dex-cache/cache.xml
improved performance of WebView for image previews, added loading dialog while page loads. Need to get PDF view working if format detected is a PDF.
Merge remote-tracking branch 'origin/master'