Added new global architecture diagram using Dia tool
and a more detailed description of each component.
Exported this diagram in SVG format.
The source code of the diagram is stored in
/doc/images_src/ folder.
Moved also the architecture.rst file from the /dev
folder to the root folder of the Watcher doc.
Change-Id: I74379390178673dcb6a043967b31e38ca9560bb3
