Use zim to maintain structured data objects

Use zim to input structured data. Aka "the poor mans database".

Structured data are forms with standard fields
- e.g. a book with Title, Author, ..
- e.g. a task with a Priority, Due Date, ...

These data objects can either be a set (e.g. a collection of books) or a graph (dependency between tasks). The later example is managed by allowing data objects to have fields linking to other data objects (e.g. Author -> author object, "depends on" -> other task object)

Requirements:
- Allow defining new data objects
- Embed forms in the page
- Cache data in the sqlite database
- Special dialog to query data objects