qt: merge ME edition into SE

(breaks PE temporarily)

Adds a Standard/Music Application Mode button to SE and thus adds the
ability to run ME scan types in SE. When in Music mode, the
Music-specific results window, details panel and preferences panel will
show up.

All preferences except scan_type become shared between app modes
(changing the pref in a mode changes it in the other mode).

Results Window and Details Panel are now re-created at each scan
operation because they could change their type between two runs.

Preferences panel is instantiated on the fly and discarded after close.

This is a very big merge operation and I'm trying to touch as little
code as possible, sometimes at the cost of elegance. I try to minimize
the breakage that this change brings.

qt/me/preferences_dialog.py

@@ -10,10 +10,11 @@ from PyQt5.QtWidgets import (
 )
 
 from hscommon.trans import trget
+from core.app import AppMode
 from core.scanner import ScanType
 
 from ..base.preferences_dialog import PreferencesDialogBase
-from . import preferences
+from ..se import preferences
 
 tr = trget('ui')
 
@@ -74,7 +75,7 @@ class PreferencesDialog(PreferencesDialogBase):
         setchecked(self.wordWeightingBox, prefs.word_weighting)
 
         # Update UI state based on selected scan type
-        scan_type = prefs.scan_type
+        scan_type = prefs.get_scan_type(AppMode.Music)
         word_based = scan_type in (
             ScanType.Filename, ScanType.Fields, ScanType.FieldsNoOrder,
             ScanType.Tag