Create some example extensions that add list columns

[Nicklas Nordborg]

BASE 3.2 will add extension points for adding more columns to the table on list pages (​http://base.thep.lu.se/ticket/1674). We should include some examples in the example code.

1. A simple example that uses regular property paths. For example, the registration date of the owner of an item. This example should be added to the list pages of all ownable items.
2. One example that demonstrates the use of a formatter by adding the email of the owner of an item. The email becomes a clickable mailto: link in the web interface.
3. A more advanced example using a custom action factory. This example display all data files related to a raw bioassay including links for viewing and downloading the file.

[Nicklas Nordborg]

(In [1596]) Fixes #376: Create some example extensions that add list columns

Added three list column examples.