1 add templating - pull request

Hi @karelOk,
Just added this pull request - for your perusal (don't approve this yet unit tests are still being created), so we can discuss more on how we want the template feature be done more correctly.

This includes a simple template feature for this plugin.
To use the template feature, simply add the `columns` attribute into the plugins shortcode.

e.g.
```
[ebayfeedsforwordpress feed="http://rest.ebay.com/epn/v1/find/item.rss?keyword=%vpt-keyword%&categoryId1=18180&sortOrder=BestMatch&programid=15&campaignid=5336886189&toolid=10039&listingType1=All&lgeo=1&descriptionSearch=true&feedType=rss" items="5" columns="4"] 
```
Notes:
- if the `columns` attribute is not set, the plugin will use its default.
- if `columns` is set to one, it'll still use the default.
- if `columns` is more than one, it'll use the `column` template.

For further development / enhancement / discussion, custom templates.