job: refactor args

[ntarocco]

• adds PredefinedArgsSchema schema class with predefined args, including
  since.
• changes JobType public/private interface to make it easier to define
  your own job types
• logs celery tasks error message and shows it in the UI
• removes unused code

[ntarocco]

Unresolved UI issues:

1. The Run form, from the list of runs, is not rendering any parameter
   

2. In the runs list, there is an extra col. In general, buttons are not rendering nicely
   

3. There is a general inconsistency between Edit buttons in the various admin panels

4. When creating a new Job, there is a Default queue, when running an existing it is called celery?
   
   

5. The last run date is not nicely formatted
   

6. When expanding an error, the column will expand to fit the text
   

7. There is a console error highlighting that the defaultSortingOnEmptyQueryString should be an object and not an array. From the DOM:
   defaultSortingOnEmptyQueryString": [{"sortBy": "last_run_start_time"}]

[carlinmack]

was there something wrong 👀

[ntarocco]

Yes, it was some weird char instead of -

[carlinmack]

It was intentionally chosen as normal n-dashes look too short: -

I prefer an em-dash: —

But went with one in between to be a bit fancy: −

Unless there is a problem with the character not displaying I don't see why not choose something that looks better