Scnodes

Release accompanying the publication.

quick patch to:
- fix a bug introduced in the previous version by the release of the 'Metrics' node group
- fix a bug in the Correlation Editor focus_camera_on() function

Adding 'Metrics' node group, containing nodes:
- add metric
- discard by metric
- plot metric

improved speed of .mrc loading
fixed .mrc rendering wrong when source data is signed integer
reset default 'view' toggle value to True for all tool windows

**Correlation Editor now contains functionality for fluorescence-guided particle picking**

_other:_
_Improved downsampling of frames at low magnification in the Correlation Editor (mipmap)
Fixed np.float deprecation warnings
Improved behaviour of scale/rotate/move w.r.t. hierarchy in the Correlation Editor
Bugfix in LoadDataNode get_img_impl_