Added “IgnoreSslError” property to the WebViewer

When set (default is not set) the WebViewer can use SSL to access web
pages with a self signed certificate. Setting it exposes you to a Man
in the Middle Attack, but on the other hand it also lets you access
pages with a self signed certificate. The security trade-off needs to
be made by the application designer.

Change-Id: I960628ebb1ea0c7c3839b8aad5170ed32fef7229
Bugfix: Properly handle zero length files in GCS code.

Change-Id: I3794f21456c9ceedea18f39f11ef278f061a6533
Modify GCS retry parameters, add more logging

Also add our own retry loop.

Change-Id: I767221df189cabb958504c51d7a04465a1ff23e5
Ensure that Built APK files are valid

If we fail to fetch a file from the Google Cloud Store, we substitute
a zero length file. This change alters this behavior to cause a fatal
error if this happens during an attempt to build a project. This
ensures that zero length assets do not wind up in a built APK file.

Change-Id: I09f841f06dacb413adb49056c73b62f65cddcaa9
Merge branch 'master' of https://github.com/mit-cml/appinventor-sources

* 'master' of https://github.com/mit-cml/appinventor-sources:
  Ensure that Built APK files are valid
  Modify GCS retry parameters, add more logging
  Bugfix: Properly handle zero length files in GCS code.
  Added “IgnoreSslError” property to the WebViewer