bug: switch to integer for the skip flag

re #498

It appears that defaults are ignored for boolean SEM parameters. Even though
the parameter was set to true in https://github.com/QIICR/dcmqi/blob/2990dbd01d1fa61c16777950732ff19dc87318e3/apps/seg/itkimage2segimage.xml#L58-L65,
the default reported by the executable was 0.

Local tests show that integer parameters do not have this problem.

Also switch to the most recent has for SlicerExecutionModel.

CMakeExternals/SlicerExecutionModel.cmake

@@ -34,7 +34,7 @@ if(NOT DEFINED SlicerExecutionModel_DIR AND NOT ${CMAKE_PROJECT_NAME}_USE_SYSTEM
 
   ExternalProject_SetIfNotDefined(
     ${proj}_REVISION_TAG
-    "62d0121dbb0fb057ebbd7c9ab84520accacec8bc"
+    "4325526343f582dd2080d0ffd93a63c8817dfb95"
     QUIET
     )
 

apps/seg/itkimage2segimage.xml

@@ -55,14 +55,14 @@
   <parameters advanced="true">
     <label>Advanced processing parameters</label>
 
-    <boolean>
+    <integer>
       <name>skipEmptySlices</name>
       <label>Skip empty slices</label>
       <channel>input</channel>
       <longflag>skip</longflag>
-      <default>true</default>
+      <default>1</default>
       <description>Skip empty slices while encoding segmentation image. By default, empty slices will not be encoded, resulting in a smaller output file size.</description>
-    </boolean>
+    </integer>
 
     <boolean>
       <name>useLabelIDAsSegmentNumber</name>