af-main: Drop capabilities of applications

af-main: Drop capabilities of applications

This removes all capabilities of applications
installed and launched by the framework.

Bug-AGL: SPEC-2006

Includes the following changes:

 * 20bf077 afm-unit.conf: Add widget specific environment
 * a44e304 afm-util: Remove legacy commands stop/resume
 * f7a3a6e API Overview: Changes to the file that introduces APIs.
 * 26dd0f8 API Reference Overview: Removed old "kristi" file, updated book
 * b4ca569 afm-unit: Restore removal of capabilities

Change-Id: I8c42d0b312aead668da03a987d0366b4ced73c70
Signed-off-by: José Bollo <jose.bollo@iot.bzh>