Reorganize navigation

Do not actually move files, so old links will still work.  Remove some
files and links to deprecated items like drift and old packages.

Towards atomisthq/product-development#320

[changelog:changed]

Author: David Dooling

docs/developer/aspects.md

@@ -22,12 +22,3 @@ The `@atomist/automation-client` package handles a number of base features for a
 * Registering generators and code transforms
 * Implementing push, event, and command listeners
 * Defining and invoking goals and goal sets
-
-## `@atomist/sdm-core`
-
-The `sdm-core` is the heart of the SDM, and has just several functions of use, dealing with the management of goals:
-
-* [goal states](/pack/goalstate/), a way to manually trigger and change the status of goals
-* [container goals](/developer/container-goals/), assisting you in creating a delivery flow with Docker images
-
-In some cases, you'll need to configure the SDM to just execute a single goal, or even perform some post-processing after the SDM is initialized. `@atomist/sdm-core` exports the `configureSdm` function to do just that.