[ENH, MAINT] MNE Scan: decouple gui from core

[gabrielbmotta]

• Add new ScanCore class, based on AnalyeCore.
• Separate plugin loading and measurement controls from main window -> now in ScanCore.
  • PluginManager and PluginSceneManager now initialized in ScanCore, shared with MainWindow
  • startMeasurement() and stopMeasurement() in MainWindow deal with GUI elements, but call on ScanCore to start/stop plugins.
• main.cpp now creates an instance of ScanCore as opposed to MainWindow.

[codecov]

Codecov Report

Merging #886 (351ed3a) into main (bd31738) will decrease coverage by 0.90%.
The diff coverage is n/a.

❗ Current head 351ed3a differs from pull request most recent head 9c0b186. Consider uploading reports for the commit 9c0b186 to get more accurate results

@@            Coverage Diff             @@
##             main     #886      +/-   ##
==========================================
- Coverage   30.20%   29.29%   -0.91%     
==========================================
  Files         452      196     -256     
  Lines       39208    11553   -27655     
==========================================
- Hits        11841     3385    -8456     
+ Misses      27367     8168   -19199     

Impacted Files	Coverage Δ
libraries/fiff/fiff_types.h	0.00% <0.00%> (-100.00%)	⬇️
libraries/fwd/fwd_bem_model.h	0.00% <0.00%> (-100.00%)	⬇️
libraries/fiff/fiff_info_base.h	0.00% <0.00%> (-100.00%)	⬇️
libraries/mne/mne_sourcespace.h	0.00% <0.00%> (-100.00%)	⬇️
libraries/connectivity/network/network.h	0.00% <0.00%> (-100.00%)	⬇️
libraries/connectivity/connectivitysettings.h	0.00% <0.00%> (-100.00%)	⬇️
libraries/rtprocessing/helpers/filterkernel.h	0.00% <0.00%> (-100.00%)	⬇️
libraries/fwd/fwd_thread_arg.cpp	1.61% <0.00%> (-88.71%)	⬇️
libraries/fwd/fwd_bem_solution.cpp	21.42% <0.00%> (-78.58%)	⬇️
libraries/mne/mne_cluster_info.h	0.00% <0.00%> (-76.48%)	⬇️
... and 288 more