Share Model merge; Merge initializers; undo/redo descs (#65)

- use "shared" pointer between Model and undo/redo instances
- adds missing initializers to Merge and Text classes
- adds checkpoints for mouse resize, barcode, and image reset.
- renames the position dialog checkpoint from Move -> Position to differentiate it from a mouse move.
- adds the Undo/Redo action descriptions to the menu items.
- adds unit tests for the Merge and Model change, and for ColorNode, RawText and TextNode.

translations/glabels_C.ts

@@ -1209,6 +1209,10 @@
         <source>Delete</source>
         <translation type="unfinished"></translation>
     </message>
+    <message>
+        <source>Resize</source>
+        <translation type="unfinished"></translation>
+    </message>
 </context>
 <context>
     <name>glabels::MainWindow</name>
@@ -1740,6 +1744,14 @@
         <source>Quick Access Toolbar</source>
         <translation type="unfinished"></translation>
     </message>
+    <message>
+        <source>Undo %1</source>
+        <translation type="unfinished"></translation>
+    </message>
+    <message>
+        <source>Redo %1</source>
+        <translation type="unfinished"></translation>
+    </message>
 </context>
 <context>
     <name>glabels::MergeView</name>
@@ -1898,10 +1910,6 @@
         <source>Set image</source>
         <translation type="unfinished"></translation>
     </message>
-    <message>
-        <source>Move</source>
-        <translation type="unfinished"></translation>
-    </message>
     <message>
         <source>Size</source>
         <translation type="unfinished"></translation>
@@ -1914,6 +1922,18 @@
         <source>Shadow</source>
         <translation type="unfinished"></translation>
     </message>
+    <message>
+        <source>Position</source>
+        <translation type="unfinished"></translation>
+    </message>
+    <message>
+        <source>Barcode</source>
+        <translation type="unfinished"></translation>
+    </message>
+    <message>
+        <source>Reset</source>
+        <translation type="unfinished"></translation>
+    </message>
 </context>
 <context>
     <name>glabels::PrintView</name>