Wrong Administration category, default product name and missing field hints in the configuration UI

Problem

RN-73 registered ReleaseNotes.Code.ReleaseNotesConfig in the wiki Administration through an XWiki.ConfigurableClass xobject, but the result has three defects:

• Wrong Administration category. The xobject sets displayInCategory to content, which is the category reserved for the categories bundled with XWiki Standard. The Release Notes application is not bundled, so its administration section must be registered under the other category, next to the other non-bundled extensions.
• A default product name is shipped. The configuration xobject ships with product set to XWiki. Nothing makes XWiki a sensible default for an arbitrary wiki: the application is meant to manage the release notes of whichever product(s) the wiki is about. Shipping that value means every administrator who does not notice it ends up creating release notes for a product literally called "XWiki". The shipped value must be empty so that the administrator has to make a conscious choice.
• No hints on the configuration fields. The section displays two fields, "Default Product Name" and "Template Reference", with no explanation of what they are used for or what format they expect (in particular, "Template Reference" expects a page reference, and it is not obvious that the field only affects newly created release notes). XWiki.ConfigurableClass displays a hint below each field label when a <classReference>_<property>.hint translation key exists, and both properties should have one.

Proposal

• Set displayInCategory to other.
• Ship an empty product value.
• Add the ReleaseNotes.Code.ReleaseNotesConfigClass_product.hint and ReleaseNotes.Code.ReleaseNotesConfigClass_template.hint keys to the ReleaseNotes.Code.Translations bundle, and set the matching hint attribute on both XClass properties so that the hints also show up in the object editor.