Plans / SlickGrid plugins - Avoid showing already selected vocabulary terms

[amiedes]

As a future improvement, we should avoid showing in the select2 options those terms that have already been added to the table.

This applies to the indicators and human resources plugin, since in the budgets plugin a budget line can appear many times.

Check if it's worth implementing it with https://select2.org/options#disabling-options

[ferblape]

This could be solved using the same approach I follow in https://github.com/PopulateTools/gobierto/pull/2455 to update the Select2 values after a cell has been updated