Be more clear in the cordova polyfills that cordova is absent, so we can
build some more polyfills once spiderOakApp is established.

Provide a polyfill for spiderOakApp.downloader.downloadFile() so we can
create favorates.  (Have to add some more so we can subsequently remove
them.)
Merge branch 'master' into issue-267-debugging-favorites-on-desktop
We can now create and remove favorites without the cordova file downloader,
eg in the desktop browser.  The file's contents is not downloaded, but we
can exercise the rest of the favorites system.
Merge pull request #271 from SpiderOak/issue-267-debugging-favorites-on-desktop

Issue 267 debugging favorites on desktop