introduced sqlite database
persist polyline element
polyline database roundtrip
refactored NoteElement equality and hashcode
polyline removable
made the database a static entity
tags and database first step
fixed a few tests
database connection string refactored
tags are removable
tagtree works again
minor test refactoring
init element filters
restructured noteelements
text database roundtrip
image database roundtrip
Merge branch 'backend' into ui_gtk_gnome
removed backend.Note from UiNote
got rid of backend.Note and autopersistence
reintroduced autopersistence