Ensure all types needed to use this crate are re-exported

[mattyg]

There are many types that are needed for actually using this crate that are not re-exported -- so you have to track them down and include them via additional holochain dependencies.

We should review other projects on github that consume this crate and check what other holochain crates they are importing for types. Also all the functions available in this crate and their input + output types.

Also not sure if we want to just glob re-export types from the holochain_*_types crates

Types needed

• SerializedBytes
• holochain_serial
• holochain_keystore::AgentPubKeyExt;
• ZomeCallUnsigned
• Timestamp
• ExternIO
• CellId
• CellInfo
• ProvisionedCell
• ClonedCell
• StemCell
• holochain_nonce::fresh_nonce