Support the Secret Service API

[woodruffw]

This is the closest thing to a standardized secret management API on Linux distributions.

Pros:

• People can use kbs2 as an integrated secret manager in any tool that knows how to use the Secret Service API

Cons:

• I have to think about D-Bus

[woodruffw]

xref: https://www.freedesktop.org/wiki/Specifications/secret-storage-spec/