API V2 compatibility

Hi Daniel,

I've added compatibility for the V2 version of the Magento API including a V2-Api-Class, a wsdl.xml and some changes in the api.xml. The V2-Api-Class basically receives an array of stdObjects with "key" and "value" properties (as described in the WSDL as type associativeEntity), transforms it to an array and passes it to the usual processing of V1.

Looking forward to hear your opinion about it.

Cheers,
Alex

Btw.: This is a soap-call i used to test the new service:

```xml
<soapenv:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:urn="urn:Magento" xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/">
   <soapenv:Header/>
   <soapenv:Body>
      <urn:apiImportImportEntities soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
         <sessionId xsi:type="xsd:string">66663dd157c1fbeb849c76b8a5d6e3d3</sessionId>
         <entities xsi:type="urn:apiImportImportEntitiesArray" soapenc:arrayType="urn:associativeArray[]">
			<item>
				<data>
					<key>sku</key>
					<value>666</value>
				</data>
				<data>
					<key>name</key>
					<value>API Product</value>
				</data>
				<data>
					<key>_store</key>
					<value/>
				</data>
				<data>
					<key>_attribute_set</key>
					<value>Default</value>
				</data>
				<data>
					<key>_type</key>
					<value>simple</value>
				</data>
				<data>
					<key>_category</key>
					<value>Furniture/Bedroom</value>
				</data>
				<data>
					<key>_root_category</key>
					<value>Root Catalog</value>
				</data>
				<data>
					<key>_product_websites</key>
					<value>base</value>
				</data>
				<data>
					<key>color</key>
					<value>blue</value>
				</data>
				<data>
					<key>cost</key>
					<value/>
				</data>
				<data>
					<key>country_of_manufacture</key>
					<value/>
				</data>
				<data>
					<key>created_at</key>
					<value>2013-05-02 18:05:11</value>
				</data>
				<data>
					<key>description</key>
					<value>API Import TEST PRODUCT</value>
				</data>
				<data>
					<key>price</key>
					<value>13.3700</value>
				</data>
				<data>
					<key>short_description</key>
					<value>API IMPORT</value>
				</data>
				<data>
					<key>size</key>
					<value>43</value>
				</data>
				<data>
					<key>special_price</key>
					<value>12.3700</value>
				</data>
				<data>
					<key>status</key>
					<value>1</value>
				</data>
				<data>
					<key>tax_class_id</key>
					<value>2</value>
				</data>
				<data>
					<key>visibility</key>
					<value>4</value>
				</data>
				<data>
					<key>weight</key>
					<value>1337</value>
				</data>
				<data>
					<key>qty</key>
					<value>1337.0000</value>
				</data>
				<data>
					<key>min_qty</key>
					<value>0.0000</value>
				</data>
				<data>
					<key>use_config_min_qty</key>
					<value>1</value>
				</data>
				<data>
					<key>is_in_stock</key>
					<value>1</value>
				</data>
				<data>
					<key>media_gallery</key>
					<value>0</value>
				</data>
			</item>
         </entities>
         <entityType xsi:type="xsd:string">catalog_product</entityType>
         <behaviour xsi:type="xsd:string">append</behaviour>
      </urn:apiImportImportEntities>
   </soapenv:Body>
</soapenv:Envelope>
```