Scaled images for print edition and fixed errors up to the beginning of layouts chapter (#19835). Also major revision of Tree, CustomField, and layouts overview.
Vaadin is not anymore using the type of GWT History support that would need the __gwt_historyFrame iframe.
Change-Id: Ibd5414ddd744b3a570bb7b23700a616ca7ee56bf
* UIDL responses only include server side timing information when not
in production mode.
* Update documentation accordingly.
Change-Id: I961d1fdc96b3d04f22254fcd13a5412f17118b42
Fixed critically broken comment blocks, broken emphasis and escaping, and some other formatting, and moved book preface, chapter structure, and index to the docs repository.