Created an activity for the ISBN scanner

The scanner pulls up another app to actually read the barcode for us
then returns it as a string. If the other app is not installed it
redirects it to the play store for the user to download
Merge remote-tracking branch 'origin/ISBN_Scanner' into Add_listing_activity

Conflicts:
	TextbookMarket/src/main/AndroidManifest.xml
	TextbookMarket/src/main/res/layout/fragment_tabs.xml
	TextbookMarket/src/main/res/values/strings.xml