Add extra DBus functions for Siril_EAA extension
Must be merged after !1221 (merged)
Adds the following:
- capturepreviewwidget can now display fits files passed in from an external source or (as default) receive frames from the capture module. Two DBus accessible functions are provided: one to switch between these modes, and a second to pass the filepath to capturepreviewwidget for display.
- Two additional DBus accessible read functions: one to get the current preview filename (eg. what is displayed as a tooltip on hover over the placeholder format textbox), and a second to get the current text entry of the placeholder format textbox.
These are used by the Siril_EAA extension to:
- Test that there are no dynamically changing placeholder tags in the file format, such that the capture filepath is a known constant.
- Obtain the capture filepath directory.
- Switch the capturepreviewwidget to display from external source.
- Pass livestacked images to the capturepreview widget for display.
- On exit of the extension the capturepreviewwidget is switched by to display captured frames.