Reorganise python build scripts for simpler CI

The purpose of this merge request are:

• Avoid dependency on another repository to perform CI testing and release generation
• Allow gateware generation from private forked repositories
• Include FPGA synthesis logs as part of the published artifacts
• Create a release on tag creation
• Make the gateware build steps directly callable from other Python scripts.

@RobertCNelson please review the Pages CI aspects