Separate out the UI from the program logic

The following are UI toolkit specific:
gtk-gui.c   - overall layout, main window of the UI
divelist.c  - list of dives subsurface maintains
equipment.c - equipment / tank information for each dive
info.c      - detailed dive info
print.c     - printing

The rest is independent of the UI:
main.c i    - program frame
dive.c i    - creates and maintaines the internal dive list structure
libdivecomputer.c
uemis.c
parse-xml.c
save-xml.c  - interface with dive computers and the XML files
profile.c   - creates the data for the profile and draws it using cairo

This commit should contain NO functional changes, just moving code around
and a couple of minor abstractions.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

uemis.h

@@ -10,6 +10,4 @@
 
 void uemis_import();
 
-extern GtkWidget *main_window;
-
 #endif /* DIVE_H */