This mod revises the admin interface used to add/remove new message icons from boards.
In a default install of SMF if you want to have a message icon available in more than one board, but less than all you have to add new icons with the same image and specify for each of these icons in which board they are visible, one by one.
With this mod the admin interface is changed in a way that for each icon you can select in which boards this icon will be available.
The option "Available In All Boards" is equivalent to the previous select option with the same name: the icon will be available in all the boards irrespective of the boards selected just below.
Selecting "Available In All Boards" will not remove the selected boards (but these will not be displayed in the "edit message icons" list, see for example "Thumb Up" in the screenshots).
In the page where all the icons are listed the column "Board" is changed to "Boards" and if the icon is available in more than one board a list of all those boards is created.
If while editing an icon all the boards are deselected as well as "Available In All Boards", the icon is removed from the database.
The mod doesn't change the database, so any change is completely compatible with a default installation of SMF.
Many thanks to Kays for the many hours he spent finding my mistakes!