Allow referencing local variable in loop

[torreytsui]

An approach is needed to allow local variable in loop to be referenced.

Example:

<htmlBlock name="around-awesome-child" selctor="#awesome-child" template="around-awesome-child.phtml">
+    <variableAssignments>
+        <variableAssignment name="product"><![CDATA[$product]]></variableAssignment>
+    </variableAssignments>
</htmlBlock>

<referenceHtmlBlock name="around-awesome-child">
    <block name="awesome-big-child" />
</referenceHtmlBlock>

[torreytsui]

This problem can be generalised and resolved by having:

• injectable block to handle <htmlBlock /> data processing
• injectable template to handle <htmlBlock /> rendering

The block and template come together and preprocess and generate a replacement of upstream template.