Merge branch 'feature/move-external-libraries-doxygen' into 'master'

Move external libraries in the doxygen tree

See merge request !3939

doc/doxygen/DoxygenDumuxLayout.xml

@@ -16,7 +16,6 @@ SPDX-License-Identifier: GPL-3.0-or-later
     <!-- The modules contains pages for each group and subpages for each subgroup -->
     <!-- Note that extra documentation can be added to groups in separate markdown files -->
     <!-- For this write @addtogroup <groupname> at the top of that markdown page -->
-    <tab type="user" url="@ref external-libraries" visible="yes" title="External libraries" intro=""/>
     <tab type="user" url="@ref examples-and-tutorials" visible="yes" title="Examples and tutorials" intro=""/>
     <tab type="usergroup" url="@ref understanding-dumux" visible="yes" title="Understanding DuMux" >
       <tab type="user" url="@ref basic-concepts" visible="yes" title="Basic concepts" intro=""/>
@@ -29,6 +28,7 @@ SPDX-License-Identifier: GPL-3.0-or-later
     <tab type="user" url="@ref flow-and-transport-in-porous-media" visible="yes" title="Flow and transport in porous media" intro=""/>
     <tab type="user" url="@ref basic-numerics" visible="yes" title="Basic numerics" intro=""/>
     <tab type="user" url="@ref python-bindings" visible="yes" title="Python bindings" intro=""/>
+    <tab type="user" url="@ref external-libraries" visible="yes" title="External libraries" intro=""/>
     <tab type="usergroup" title="Developer documentation">
       <tab type="user" url="@ref dumux-and-dune" visible="yes" title="Dumux and Dune" intro=""/>
       <tab type="user" url="@ref developing-dumux" visible="yes" title="Developing Dumux" intro=""/>