A new phy scope based on ImGui and ImPlot. This scope uses a different concurrency model than previous
scopes.

The PHY thread writing the data first checks if the data is ready to be written. If its not, nothing is copied.
The GUI thread reads data if available and marks it ready to write. This makes sure that the PHY threads are not
busy copying data that would never be displayed.

Some of the scopes also have a freeze functionality that further limit the amount of data that needs to be copied
from PHY threads. If a scope is "frozen" it still allows the user to explore the data using plots zoom/pan functions
but doesn't cause PHY threads to perform extra writes on the displayed data.

A compile option was added to enable/disable the scope. Use cmake -DENABLE_IMSCOPE=ON to enable the scope.

Update CXX standard to 17; it is required by some libraries (e.g., dear imgui). The oldest gcc version in
use by a distribution supported is Ubuntu 20, which has gcc 9.4 with c++17 support.