add boot_audio

yeah let's annoy

 Changes to be committed:
	new file:   prebuilt/media/boot_audio.mp3
removed emailgoogle and exchange2google

unneeded since they build from source

 Changes to be committed:
	modified:   .gitignore
	deleted:    prebuilt/gapps/system/app/EmailGoogle.apk
	deleted:    prebuilt/gapps/system/app/Exchange2Google.apk