Don't display disabled block categories and items

Here's a patch that reflects the current state of the merge request, with fields to set the status on the block and category forms.

Thanks @rlhwk for the patch and @yonailo for the useful addition.

I slightly adapted the patch:
- Instead of doing the filtering in the foreach loops, I simply updated the ->loadMultiple() queries to use ->loadByProperties(['status' => TRUE]); instead.
- I added the status (Enabled/Disabled) as columns in the block and categories list so people don't need to check the Edit form to get the status.

I will create a follow-up task to have Enable / Disable link in the operation links.

Wonderful, thanks!

Automatically closed - issue fixed for 2 weeks with no activity.