MacroPreprocessor: resolve Button type inputs

When calling a command from a macro, we usually don't want to show a UI dialog.

If the called command contains inputs of type Button, we resolve these without setting them,
as we assume that buttons and their callbacks provide some interactivity that is not required
when running from macro.

See #239 for some discussion.

src/main/java/net/imagej/legacy/plugin/MacroPreprocessor.java

@@ -40,6 +40,7 @@
 import org.scijava.module.process.PreprocessorPlugin;
 import org.scijava.plugin.Parameter;
 import org.scijava.plugin.Plugin;
+import org.scijava.widget.Button;
 
 /**
  * Populates the module's input values, when the command is invoked from an
@@ -67,12 +68,16 @@ public void process(final Module module) {
 		if (!ij1Helper.isMacro()) return;
 		for (final ModuleItem<?> input : module.getInfo().inputs()) {
 			final String name = input.getName();
+			final Class<?> type = input.getType();
 			final String value = ij1Helper.getMacroParameter(name);
 			if (value == null) {
 				// no macro parameter value provided
+				if (type.equals(Button.class)) {
+					// skip if input is a button
+					module.resolveInput(name);
+				}
 				continue;
 			}
-			final Class<?> type = input.getType();
 			if (!convertService.supports(value, type)) {
 				// cannot convert macro value into the input's actual type
 				continue;