Since C++17, the introduction of deduction guides for locking facilities
means that we no longer need to hardcode the mutex type into the locks
themselves, making it easier to switch mutex types, should it ever be
necessary in the future.
Reduces the potential amount of rebuilding necessary if any headers
change. In particular, we were including a header from the core library
when we don't even link the core library to the web_service library, so
this also gets rid of an indirect dependency.
Like with TelemetryJson, we can make the implementation details private
and avoid the need to expose httplib to external libraries that need to
use the Client class.
* WebService: Verify username and token; Log errors in PostJson
* Fixup: added docstrings to the functions
* Webservice: Added Icons to the verification, imrpved error detection in cpr, fixup nits
* fixup: fmt warning
