Relation comments

[GerZah]

This version enhances Item Relations by adding the possibility to add a comment to every relation that you create.

First example:

• Let's say you use two item types, "City" and "Person".
• Now you create a user-defined relation named "Mayor Of", which you intend to use to specify that a person was mayor of a city.
• However, over time, the city had multiple mayors.

The comment field will give you the chance to relate multiple persons, and leave a tiny note inside the relation, like perhaps a starting year.

Second example:

• Let's say you create an item type called "Literature", which will hold books and scientific papers.
• Now you create a relation labelled "Mentioned in" to be able to relate pretty much any item type with your pieces of literature.
• Especially books might cover multiple mentions, and relating an item only to the literature as a whole does not suffice. However, now you can add a chapter and/or page number to create a more specific reference.

The option to enter relation comments is inactive by default, but you can easily activate it in the plugin settings.

---

My commit 52b44fe titles the plugin version 2.0.2.1, as it needs to add an additional column "relation_comment" to the item_relations_relations table compared to the regular 2.0.2 master.

It (obviously) merges nicely with my former pull request with the item ID selector (commit 144f1cd). It should be possible to merge it with a clean 2.0.2 master, but there might be tiny dependencies.

• You can easily ignore the CSS patch, as this file does not yet exist in the master branch. It simply shrinks the width of the relation selector box so the relation table fits into the editor.
• Hunk 5 in item_relations_form.php might not merge easily, as both passages before and after it were already modified in 144f1cd. If so, simply fit it in as an additional before the "n/a" one.