Major Compatibility Bugfix Release

What's Changed

• Major compatibility fix for any PyNWB file generated with a Units table by @lawrence-mbf in #506
• add optogenetics tutorial by @bendichter in #497
• Create Project Actions by @mavaylon1 in #485
• Remove international datestring parsing for version checks by @lawrence-mbf in #509

Full Changelog: v2.6.0.1...v2.6.0.2