Allow Anonymous Overview Creation

[ecc521]

There should be an easy way to turn a gauge into a river (or at least create a river for that gauge).

[ecc521]

This shouldn't be just for gauges - there needs to be a way for people to create overviews and rivers in general.

[ecc521]

This should probably be done by using a Google Apps Script running in script owners context that creates a file, in a separate directory that requires review.

[ecc521]

Rivers can now be anonymously created.