a few refinations
start refactoring the sitemap element design and implementations
Type renamed to ElementType
add new interfaces for the sitemap mental model
add new elements
refine NonNestableElement
1. add the 'public' modifier for each method in each interface; 2. move ItemImpl.java into the items.impl package
remove the 'toXtext()' method from the 'Element' interface
move ConfigImpl into ConfigBuilder as a private static inner class
1. refine to 'org.openhab.designerx' the groupId of dependencies module; 2. add the modelrepository module
delete beans.xml
add SitemapReader
modify SitemapReader and add SitemapWriter
SitemapReader and SitemapWriter is designed to be bound to a sitemap once created.
the 'model' module will provide the instances of the interfaces in the way of builder/factory
correct the name of ColorPickerImpl to ColorpickerImpl
add new builders