Doxygen tweaks.

Add Logo, so it appears on the web pages.
Disable tree view as it has a bug that prevents the hyperlinks working well, and WIT uses those hyperlinks.

audacity.dox

@@ -51,7 +51,7 @@ PROJECT_BRIEF          =
 # pixels and the maximum width should not exceed 200 pixels. Doxygen will copy
 # the logo to the output directory.
 
-PROJECT_LOGO           = 
+PROJECT_LOGO           = images/AudacityLogo.png
 
 # The OUTPUT_DIRECTORY tag is used to specify the (relative or absolute) path
 # into which the generated documentation will be written. If a relative path is
@@ -1438,7 +1438,7 @@ DISABLE_INDEX          = NO
 # The default value is: NO.
 # This tag requires that the tag GENERATE_HTML is set to YES.
 
-GENERATE_TREEVIEW      = YES
+GENERATE_TREEVIEW      = NO
 
 # The ENUM_VALUES_PER_LINE tag can be used to set the number of enum values that
 # doxygen will group on one line in the generated HTML documentation.