Adds table description (ajax retrieved)

This PR adds the chance of including an html element which will contain the table's description. If you add

```
<div class='well' id="tabledescription"></div>
```

to the html template, the ```initialize``` method of MapsLib will make an ajax request and fill the div with information about the table such as
* title
* description
* link to original table
* attribution
* attribution link

if no such div is found then no request is made