Update the main page documentation and architecture image to reflect …

…current situation

Use the SVG directly in the documentation, with the PNG as a fallback

cmake/Doxyfile.cmake

@@ -802,7 +802,7 @@ RECURSIVE              = YES
 # Note that relative paths are relative to the directory from which doxygen is
 # run.
 
-EXCLUDE                = @PROJECT_SOURCE_DIR@/src/core/external 
+EXCLUDE                = @PROJECT_SOURCE_DIR@/src/core/external
 
 # The EXCLUDE_SYMLINKS tag can be used to select whether or not files or
 # directories that are symbolic links (a Unix file system feature) are excluded
@@ -1123,7 +1123,9 @@ HTML_EXTRA_STYLESHEET  =
 # files will be copied as-is; there are no commands or markers available.
 # This tag requires that the tag GENERATE_HTML is set to YES.
 
-HTML_EXTRA_FILES       = @PROJECT_SOURCE_DIR@/doc/jquery.js
+HTML_EXTRA_FILES       = @PROJECT_SOURCE_DIR@/doc/jquery.js \
+                         @PROJECT_SOURCE_DIR@/doc/images/stellarium-architecture.svg \
+                         @PROJECT_SOURCE_DIR@/doc/images/stellarium-architecture.png
 
 # The HTML_COLORSTYLE_HUE tag controls the color of the HTML output. Doxygen
 # will adjust the colors in the stylesheet and background images according to
@@ -1987,7 +1989,7 @@ INCLUDE_FILE_PATTERNS  =
 # recursively expanded use the := operator instead of the = operator.
 # This tag requires that the tag ENABLE_PREPROCESSING is set to YES.
 
-PREDEFINED             = 
+PREDEFINED             =
 
 # If the MACRO_EXPANSION and EXPAND_ONLY_PREDEF tags are set to YES then this
 # tag can be used to specify a list of macro names that should be expanded. The