Sample data

[phockett]

Quick additions for QM3

• Added general data downloader, 7464c2e
• Added OCS sample data for QM3 use. matrix elements d598d4f and ADMs 94bc0e2. This is as per ePSdata https://phockett.github.io/ePSdata/OCS-preliminary/OCS_orbs8-11_AFBLMs_VM-ADMs_140122-JAKE_tidy-replot-200722_v5.html, but should be wrapped/updated and pushed to main pages. (See also ePSdata interface #31.)