Plugins

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This adds the ability to extend py4DGUI using a plugin mechanism. Classes living in the py4d_browser_plugin namespace and possessing certain attributes are automatically discovered and loaded. Currently the interface is minimal, and plugins have complete access to the DataViewer object, but more over time the interface will become more strictly prescribed. As this develops, all non-core features (including ones currently available in the browser) will be implemented as plugins, and this should also help to clarify how to make an effective interface between the core and the plugins.

To-dos:

• Re-implement calibration menu as internal plugin
• Re-implement tcBF as internal plugin
• Re-implement EMPAD2 raw reader as external plugin
• Create API for plugins to access detector ROI information
• Update calibration and tcBF plugins to use ROI API
• Implement signals/slots for various update conditions to enable better live analysis plugins

The intention is that this will allow for greater flexibility when adding advanced analysis features as well as the ability to control acquisition hardware directly in the GUI. This also helps maintain a clean separation of state between the core functionality and any ancillary features.

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In the interests of finally getting these new features out there, I am going to release this without making the updates to the signals/slots for live plugins.