ENH: Add the ability to create custom actions

[bananarama92]

Add the ability to create up to 16 custom characters actions. The following aspects of the actions should be configurable:

• The name
• The action's chat message
• The action's icon
• The maximum value that it can increment the arousal bar
• The ability to specify activity prerequisites
• On which slots the action can be performed
• Whether the action can be performed on yourself, on others or both
• The ability to automatically set a facial expression. Note that this might be reserved for a later v0.7.x patch; as of the moment of writing it's not clear whether any of the popular addons (i.e. BCX and/or FBC) store expressions in their outfit codes.

[bananarama92]

• The ability to specify activity prerequisites
• On which slots the action can be performed

For these two a drop-down menu with check boxes would be ideal. The BC ElementCreateDropdown() function would probably be a good starting point here.