GUI: Add HeaderBar && Views

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Add contacts view

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Git ignore *.sqlite

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Refactor ContactView to multiple classes

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Make group name/address label editable

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Implement Add group

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Implement Add subgroup

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Always save new group

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Implement Remove group

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Add support for drag and drop

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Use Gtk.Application & Gtk.ApplicationWindow

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Use Gio.Actions

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>