[Feat] Add a macro tab to actions / items

[Pjb518]

Add a new tab to actions and possibly items where users can define macros à la the Item Macro module. Users will be able to select whether the macro runs before or after the item activation, or whether it replaces the default activation entirely.

When a macro is defined for a given action or item (the field is not empty), the macro will be execute when the parent item is activated.

We should also look into possibly providing a simpler editor that allows for syntax highlighting to make it easier to write macros in the system.

[Pjb518]

Tentatively added this to the 0.9.x release cycle. It may be something for 1.0.0 instead.