Web api expansion

[JohnDMcMaster]

This large patch encompasses a number of projects:

• Replace fledgling Instrument API with Subsystem API
• Subsystem API includes first class "RPC" support via "function_ts()" to bind to web API
• Plugins can now be loaded via .pyuscope as Subsystem instruments. Each one gets its own scripting engine
• Expanded Scripting API with new functions like system_status()
• Demo using Scripting to call a Subystem function in another script. Not currently bound / tested to web API but will be soon
• Web API: add a number of functions such as autofocus
• Web API: code cleanup / refactor

Fixes https://github.com/Labsmore/pyuscope/issues/440

Fixes https://github.com/Labsmore/pyuscope/issues/435

Fixes https://github.com/Labsmore/pyuscope/issues/433

Scripting API but not web API is present now for: https://github.com/Labsmore/pyuscope/issues/438

Adds untested scripting support for: https://github.com/Labsmore/pyuscope/issues/437

[JohnDMcMaster]

Startup now prints a version string: "pyuscope starting (version v4.5.0-5ddc39d1-dirty)"