1) Text Editors for Mac: TextMate (often called 'best editor for Mac in the world', not free), BBEdit (not free), TextWrangler (free) etc.
2) Poedit is available for Mac, it should work, just try it again, it is the safest way to edit .po files and create non-corrupted .mo exports, .mo files are created/updated automatically when you save your .po file you currently have opened in editor.
3) you didn't make much mess on github, you only messed up your copy
/branch. You can delete that branch any time, just select jobs_attribute plugin and appropriate (yours) branch, look at the right lower part of the screen and see Settings, there at the bottom you will see big red Delete...
4) Comits can also be deleted if you are the owner, you will have something like this
5) don't panic
and blame too much yourself, we all learn here, nobody knows everything...
also, devs are not 24h service neither here or on github. Relax