Add OSGi metadata to Kazuki, currently all packages are exported.

Note: I made the implementation bundle a fragment of the API bundle so they get merged together at runtime. 

This is because they each contribute different classes to the same packages, for example `io.kazuki.v0.store.schema.SchemaStore` from the API bundle, and `io.kazuki.v0.store.schema.SchemaStoreListener` from the implementation bundle. (This is known as a split package in OSGi, where the package content is split across multiple bundles.) The alternative solution was to use Require-Bundle, but that takes more effort and involves the use of import attributes.