Add support for Actions within plugins

[peternandersson]

** This PR requires a bit of cleanup before it is ready to be merged **

This PR adds support for plugins to trigger actions in workbooks and for workbook actions to call functions within a plugin using the notions of action trigger (plugin -> workbook) and action effect (workbook -> plugin).

This PR adds the following config options:

• action-trigger: This corresponds to an Action selectable within workbook UI by selecting a Plugin, navigating to the Actions sidebar, and adding an Action.
• action-effect: This corresponds to a new Action type within workbooks. This is selectable by selecting any Action in a workbook, and selecting Trigger plugin, then selected the configured action-effect

It adds the following functions:

• triggerAction: This function, when called with the config object, will trigger all Actions configured in the workbook UI under the current plugin element
• registerEffect: This function registers a handler for when a certain Action, as configured in UI, is triggered.
• unregisterEffect: This function will remove any registration (done with the function just above) associated with the id passed in (considering moving this to be a return value of registerEffect above)

In addition, it adds the following react hooks:

• useActionTrigger: This function returns a callback that triggers the action associated with the id passed in
• useActionEffect: This function takes in the associated config item, and handles the unsubscribe on unmount