Change forge-errai link to v2.0.0.Beta1 tag.
Set width of getting started screenshots to 650.
Lots of doc improvements.

Linked to Errai Forge Addon tag (Beta1).
Add plugin tips and general editting up to Marshalling section.
More doc improvments.

Add plugin tips and manual setup notes up to errai navigation.
Move all setup/configuration instructions in those sections to single
location.
Finish restructuring of docs up to Configuration section.
Reorganize Configuration section of docs.
Commit change to docbook reference.xml