FontAwesome update on CKAN 2.7

[torfsen]

CKAN 2.7 uses FontAwesome 4, and there are multiple changes from version 3.

For ckanext-pages, some of these have already been taken care of by #51, but it seems that there are still some things to fix. For example, we use the edit icon from FA 3, which is now called pencil-square-o. In particular, we need to check the ckan_icon arguments to map_connect and the icon arguments to the link_for template macro.

As with #51 we need to maintain backwards-compatibility with earlier versions of CKAN. This can be done by using both the new and old FA CSS classes (e.g. class="icon-edit fa fa-pencil-square-o") or by using a custom helper function. In the latter case, we should use one helper function for all icons (pages_get_icon) instead of adding a separate helper function for each icon.

[nykc]

Issues icon is also missing along with a few others.
I am currently using CKAN 2.8.2