Create, view and edit instance

[lecoqlibre]

An instance is a WordPress object referring to a Weblate instance hosted on a distant server.

See #1 for managing instances.

An instance is composed of:

• a name: used to refer to this instance inside WordPress
• an API base URI: the URI of the Weblate API to use (entry point)

Once an instance is registered, the administrator can select every Weblate project it wants to use for translating the website. To do this, each Weblate project is listed with a checkbox Use this project for translating. This will create if necessary when saving the instance a WordPress project object for any Weblate project "used for translating" (see #2).

Multiple Weblate instance with the same API base URI can be registered to allow fine control over instances.