Speed up editing flag configuration properties

[Abrynos]

Purpose

Speed up workflow for the user when editing flag-enum configuration properties

Solution

Instead of having to click the Add button every time I want to add a value to a flag enum (e.g. for the config property BotBehaviour) I have to press the add-button. I'd like the value to be automatically added when selecting it from the dropdown.

Alternatives

Do nothing and leave it at two clicks necessary for each value.

[Botan626]

This issue could be combined with #1442 and dropdown menu could have checkboxes with such structure:

Instead of 'Every day' it could have All option and instead of 'Last Weekday in month' it could have None option. And property values instead of days of course. No need for Add button then.