Add interchange helper script for REPL mode

[kboronski-ant]

A small script providing useful features when using python in REPL mode to explore interchange device data.

Usage:

export FPGA_INTERCHANGE_SCHEMA_PATH=/path/to/interchange/schema/repository
python3 -i interchange.py /path/to/device/file
> # run your commandsd

The scripts loads the device, assigns it to the `device` variable in global scope and creates some useful functions for navigating through the device.