A: New URL scheme

This turns ```#storage-details?type=drive?id=Foo?machine=bar``` into ```#/bar/storage-details?type=drive?id=Foo```.

This is turned into ```#/bar/storage/drive/Foo``` when Storage becomes a external page in an iframe.

The next step is to remove the need for PageExternal.

In my opinion, if we're making this public API:

 * The public API should be simpler, something like:
```
cockpit.page.path
cockpit.page.options() /* getter and setter, similar to jQuery .text() and such*/
$(cockpit.page).on("changed") ...
```
 * The public API needs to be documented in the guide.
 * The API needs unit tests, see #1399 for examples of tests both with and without qunit, whatever you prefer.