Fix distcheck
Remove some unnecessary virtuals.
Make some protected API private, to simplify some API.
Field Definition: Move Default formatting into a separate window.

* glom/mode_dsign/fields/dialog_fielddefinition.[h|cc]:
* data/ui/developer/window_field_definition_edit.glade:
  Move the Default Formatting notebook tab into:
* glom/mode_design/fields/dialog_defaultformatting.[h|cc]:
* data/ui/developer/window_default_formatting.glade:

* glom/utility_widgets/adddel/adddel.[h|cc]:
  Add signal_user_requested_extra.
* glom/utility_widgets/adddel/adddel_withbuttons.[h|cc]:
  Add set_edit_button_label() and set_extra_button_label()
  and override show_all_vfunc() to not show the extra button if
  it has no label.

* glom/mode_design/fields/box_db_table_definition.[h|cc]:
  Use the new button to show the new dialog.
Remove some debug output
Update POTFILES.in
Make some dialogs less high.

* data/ui/developer/box_formatting.glade:
  Arrange the Related Records choices in a grid, making the
  dialog wider, but less tall.
  Likewise, arrange the last two checkboxes horizontally instead
  of vertically.
* data/ui/developer/dialog_layout_field_properties.glade:
  Move the Formatting to the entire right-hand side of the dialog.
  This leaves ugly empty space at the left of the dialog,
  but it makes the dialog less high.
User Guide: Fix make dist.

* docs/users-guide/C/glom.xml: Rename this to index.docbook.
* docs/user-guide/Makefile.am: List the index.docbook and legal.xml
  files in HELP_FILES, not using HELP_EXTRA. This is
  what gnome-system-monitor does and it seems to fix the problem
  with unbuilt stamp files.
Find ID Dialog: Fix the expansion.
New Related Record dialog: Fix expansion and title.