The previous automatic ID generation caused problems with the usage of
adhoc_storage constructors outside RPC handler code (e.g. during
conversions). It makes more sense for IDs to be assigned by
a server-centric adhoc_storage_manager.

This commit separates the functionality of managed_rpc_type<T> into
dedicated lifetime management types and conversion functions. This
makes for clearer the code since it is now possible to know when
a conversion is performed.

Lifetime management for C-types is now done with the managed_ctype<T>
types, which act only as holders of dynamically allocated C types and do not
perform any type conversions whatsoever.

Type conversions are now done with the T1 convert(T2 obj) family of functions.
When converting from CXX to C API types, these functions effectively
return instances of the appropriate managed_ctype<T>s. If one wishes to
relinquish ownership of the content of the managed_ctype<T> (e.g. to
pass it to a pure C function that will release it), this can be done
with the managed_ctype<T>::release() function.

- `scord` daemon now has its own directory in `src/scord`
- `scord-ctl` daemon now has its own directory in `src/scord-ctl`
- library code now lives under the  `lib` directory
- public rpc definitions now live in `src/lib/rpcs/`
- private rpc definitions for each daemon now live in
  `src/scord/rpcs/` and `src/scord-ctl/rpcs/`, respectively
- `config`, `logger`, and `network` code now live under the `common` directory

Also, rpc definitions have now moved into the `src/rpc` folder and have
their own CMake target