improvements to attachable content module

[holtzermann17]

In #252 I didn't get around to adding the AJAX feature.

There are other things like:

• pre-populating the search box [ ]
• allowing people to autocomplete on the name of an article if they know it [✓]
• filtering by owner or other aspects of permission [ ]

As mentioned on that ticket, tips for AJAX stuff are here: http://www.computerminds.co.uk/drupal-code/make-link-use-ajax-drupal-7-its-easy

Note that for Groups would be to only "find" articles that you actually have permission to attach (this is an application of filtering based on permission).

[holtzermann17]

This is probably too much to ask for in the beta testing period, maybe we can aim for it a bit later in the year cf. https://github.com/holtzermann17/planetmath-docs/issues/13