This creates an application with a menu and toolbar using a vertical
GtkBox and adds the docking manager to a position in the middle of the
GtkBox.

The layout looks like the following:

  +------------+
  |    Menu    |
  +------------+
  |   Toolbar  |
  +------------+
  |  [Docking] |
  +------------+
  | Status bar |
  +------------+

Fill this area with a green colour.

This draws the peppers.png image to the Cairo context in the top-left
corner.

Buttons for navigating to the:
 - First page
 - Previous page
 - Next page
 - Last page

Uses `pdfinfo` to get the number of PDF pages and `mudraw` to get the
current page as a PNG file.

The next and previous pages can be accessed via the buttons and there
are buttons to jump to the first and last pages.

Added text entry using Glade. Setup the activate signal to use the
callback to set the page number. When the page number is changed,
the number in the entry field is changed to match the current page.

Added text entry for setting and viewing page number.

Set the main window title to the PDF filename

There is still an issue with size of the scrolling window because we do
not have the exact dimensions of the PDF page.

This tells the outer scrolling frame how far to scroll in both
directions.

Scrolling drawing area