Improves page layout section logic so that sections can be modified or extended.
Adds @ToolUi.CodeType annotation.
Adds GridSection.
Fixes compile error from previous commit.
Changes RenderTag to accept any object as gridTemplate.
Merge branch 'master' into feature/css-grid

Conflicts:
	tool-ui/src/main/webapp/style/cms.less
Replaces GridSection.children which had to be referenced by a numerical index with GridSection.Area that can be referenced by name and contain multiple contents.
Adds a note about /height syntax in GridSection.heights.
Changes admin/templates to show add section links.
Adds internalName to Section.
Changes GridSection rendering to use shareable sections and main content as areas.
Adds Page.defaultContent.
Adds request attributes to grid's contents when rendering.
Adds <cms:layout> tag that generalizes previous grid template additions.
Fixes ClassCastException when ContainerSection.getChildren references an orphaned object.
Changes SEO and URL widgets to show up if the object is an instance of a subclass of Page.
Fixes NPE when section type info is lost in admin/templates page.
Changes LayoutTag to use the new HtmlGrid object from Dari.
Changes Page.getAreas to return a map instead of a list.
Removes PageFilter.Static.getSection and replaces it with the sections request attribute.