Toggle: bind plugin events outside of init

This makes the events available to other plugins of the framework
without needing the plugin initialized on the page (#3026).
data-picture: bind plugin events outside of init

1. This makes the events available to other plugins of the framework
without needing the plugin initialized on the page (#3026).
2. Also adds `vapour.getMode()` call to plugin's dependency loading
Merge pull request #3057 from patheard/event-binding

Moved event binding outside of plugin.init()