ENH: Doxygen use svg and mathjax

Replace the Doxygen PNG object hierarchy figures with SVG files. Also
replace rendered math latex with mathjax javascript.

The size of the HTML Doxygen is reduced from 2.7GB to 884MB a 67%
reduction in size.

Utilities/Doxygen/CMakeLists.txt

@@ -140,11 +140,8 @@ if (ITK_BUILD_DOCUMENTATION)
   file(COPY workbox-cli-config.js serviceWorker.js.in
     DESTINATION ${ITK_BINARY_DIR}/Utilities/Doxygen/)
 
-  find_package( LATEX )
 
-  if( NOT LATEX_COMPILER )
-    message( "Warning: LaTeX not found. Formulas will not be generated in documentation." )
-  endif()
+  find_package( LATEX )
 
   # Custom command to generate a examples page which include all ITK examples
   add_custom_command( OUTPUT "${ITK_BINARY_DIR}/Documentation/Doxygen/Examples.dox"

Utilities/Doxygen/doxygen.config.in

@@ -1533,7 +1533,7 @@ FORMULA_TRANSPARENT    = YES
 # The default value is: NO.
 # This tag requires that the tag GENERATE_HTML is set to YES.
 
-USE_MATHJAX            = NO
+USE_MATHJAX            = YES
 
 # When MathJax is enabled you can set the default output format to be used for
 # the MathJax output. See the MathJax site (see:
@@ -1556,7 +1556,7 @@ MATHJAX_FORMAT         = HTML-CSS
 # The default value is: https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/.
 # This tag requires that the tag USE_MATHJAX is set to YES.
 
-MATHJAX_RELPATH        = http://www.mathjax.org/mathjax
+MATHJAX_RELPATH        = https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.7/
 
 # The MATHJAX_EXTENSIONS tag can be used to specify one or more MathJax
 # extension names that should be enabled during MathJax rendering. For example
@@ -2476,7 +2476,7 @@ DIRECTORY_GRAPH        = @ITK_DOXYGEN_DIAGRAMS@
 # The default value is: png.
 # This tag requires that the tag HAVE_DOT is set to YES.
 
-DOT_IMAGE_FORMAT       = png
+DOT_IMAGE_FORMAT       = svg
 
 # If DOT_IMAGE_FORMAT is set to svg, then this option can be set to YES to
 # enable generation of interactive SVG images that allow zooming and panning.