Docs need updating from PhoneGap to Cordova

[Bryce Curtis]

I see several JIRA issues about updating the docs/guides and renaming
assets to Cordova for 1.6.0, but they are all open.  Is anyone working on
these?   If not, then I can convert everything to Cordova - maybe mention
that PhoneGap and Cordova are sometimes used interchangeably (since some
images still have PhoneGap and download is from phonegap.com.