Upon startup, a registry (dict) is initialized for each Component
module. Then, everytime a Component is validated/invalidated, this registry is
updated.

This avoids looking whether a Component exists in ZODB/Catalog and is
validated in Component Tool on every imports or when loading a Component,
instead the registry is used. Moreover, the Catalog was used before as the
Component are matched by their reference and their validation state, thus
making bootstrap tricky.