Move credential token and secret into variables.

Allow 3rd party apps, like PhoneGap/Cordova, to execute inline script
and get the token and secret key easier.
Remove one unhelpful stack frame from Deps

Instead of `callWithNoYieldsAllowed` which calls a function
within (introducing a new stack frame that doesn't absolutely
nothing on the client), we now use `withNoYieldsAllowed` that
returns a new function that then gets called.

Since Deps is used all over the place, and in particular
in Blaze, this makes it much easier to look at the stack
trace when stopping in a debugger (for example, when a helper
gets re-executed).

Motivated by the Blaze manual.
Fix double-removal of elements.

Change the unused `viaBackend` flag to `elementsAlreadyRemoved`, and set
the flag in two places: 1. when we remove things from a DomRange
immediately after calling `removeNode`, and 2. when DomRange is notified
that an element has been removed via DomBackend.

The motivation is that re-enabling undocumented animation hooks revealed
that we were trying to remove elements twice: once from `removeNode`,
and once from `nodeRemoved` (via `membersRemoved`).
Merge branch 'via-backend-fix' into devel
Fix css urls rewrite in application code.

An attempt to fix #2106
Tests for CSS url rewrites fixed to the new implementation

i.e. rewrite only style sheets taken from /packages/ folder