Add trigger options to libScope and update interface/memory management to be faster at reading data

libScope:

• Add simple trigger setup, trigger position and variable number of samples
• PS6000 buffers are now initialized when a channel is enabled
• Change PicoScope::run() to take a reference to final storage instead of creating new structures

pbv2:

• Update scope functionality to use new PicoScope::run()
• Add proper dependencies on GPIB and Scope in CMakeLists

examples:

• Add scope_test example for how to use the PicoScope library
• add pixel_scope_run for their testbeam clock monitoring