About plugins

Plugins are components with a GUI that perform some action for Krita.
Note that plugins are only loaded when a KisView is constructed; note 
also that every plugin is reloaded when a new KisView is created.

Plugins are _not_ allowed to depend on each other. You may _not_
#include a header file from a plugin anywhere but in that same plugin.
You can however choose to group a cluster of related functions in
one plugin, like with the selection tools.
