part 2 basedoc: move BaseDoc.py to /gen/plug/docgen and add /gen/plug/docbackend

that was missing in part 1 
 Still to come: makefiles and splitting new basedoc.py in small files


svn: r12591

src/plugins/textreport/CustomBookText.py

@@ -44,7 +44,8 @@ from gettext import gettext as _
 from gen.plug import PluginManager
 from gen.plug.menu import TextOption
 from ReportBase import Report, MenuReportOptions, CATEGORY_TEXT
-import BaseDoc
+from gen.plug.docgen import FontStyle, ParagraphStyle
+from gen.plug.docgen.basedoc import (FONT_SANS_SERIF, PARA_ALIGN_CENTER)
 
 #------------------------------------------------------------------------
 #