add Mapmerge tool, update unit input to freetext

Mapeditor/Mapeditor.html

@@ -862,11 +862,7 @@ function renderParamBlock(taskKey, paramKey, param) {
         </div>
         <div class="form-group">
           <label>Unit</label>
-          <select id="p-${taskKey}-${paramKey}-unit">
-            ${['minutes','hours','days','weeks',''].map(u => 
-              `<option value="${u}" ${param.unit===u?'selected':''}>${u||'(none)'}</option>`
-            ).join('')}
-          </select>
+          <input type="text" id="p-${taskKey}-${paramKey}-unit" value="${esc(param.unit||'')}" placeholder="minutes, reps…">
         </div>
         <div class="form-group">
           <label>Timer info</label>