Add suggested values for every mapping config parameter

Set volume to homogeneous index 0 and set boundaries to increasing
indices

doc/default_files/common-parameters.xml

@@ -84,6 +84,7 @@ adding an empty line, make text **bold** or ``monospaced``.
         Leave empty or set to ``None`` for global mappings.
       </definition>
       <values> path </values>
+      <suggestion> None </suggestion>
       <comment> This category is only used for 'rectangular' grids </comment>
     </parameter>
 
@@ -92,6 +93,7 @@ adding an empty line, make text **bold** or ``monospaced``.
         mapping from cell to medium index. May specify a global index for the
         entire volume if its value can be parsed as ``int``.
       </definition>
+      <suggestion> 0 </suggestion>
       <values> path or int </values>
     </parameter>
 
@@ -100,6 +102,7 @@ adding an empty line, make text **bold** or ``monospaced``.
         boundary condition indices. May specify a global index for the
         boundary if its value can be parsed as ``int``.
       </definition>
+      <suggestion> 0 </suggestion>
       <values> path or int </values>
     </parameter>
 
@@ -108,6 +111,7 @@ adding an empty line, make text **bold** or ``monospaced``.
         boundary condition indices. May specify a global index for the
         boundary if its value can be parsed as ``int``.
       </definition>
+      <suggestion> 1 </suggestion>
       <values> path or int </values>
     </parameter>
 
@@ -116,6 +120,7 @@ adding an empty line, make text **bold** or ``monospaced``.
         boundary condition indices. May specify a global index for the
         boundary if its value can be parsed as ``int``.
       </definition>
+      <suggestion> 2 </suggestion>
       <values> path or int </values>
     </parameter>
 
@@ -124,6 +129,7 @@ adding an empty line, make text **bold** or ``monospaced``.
         boundary condition indices. May specify a global index for the
         boundary if its value can be parsed as ``int``.
       </definition>
+      <suggestion> 3 </suggestion>
       <values> path or int </values>
     </parameter>
 
@@ -132,6 +138,7 @@ adding an empty line, make text **bold** or ``monospaced``.
         boundary condition indices (3D only). May specify a global index for
         the boundary if its value can be parsed as ``int``.
       </definition>
+      <suggestion> 4 </suggestion>
       <values> path or int </values>
       <comment> Only in 3D </comment>
     </parameter>
@@ -141,6 +148,7 @@ adding an empty line, make text **bold** or ``monospaced``.
         boundary condition indices (3D only).  May specify a global index for
         the boundary if its value can be parsed as ``int``.
       </definition>
+      <suggestion> 5 </suggestion>
       <values> path or int </values>
     </parameter>
   </category>