downscale nonrotated spreads to 2x device width (#1147)

* don't downscale nonrotated spreads

* maximum 2x screen downscale

* only downscale if needed

* don't do for kindle scribe

kindlecomicconverter/comic2ebook.py

@@ -1547,6 +1547,7 @@ def makeBook(source, qtgui=None, job_progress=''):
         GUI.progressBarTick.emit('1')
     else:
         checkTools(source)
+    options.kindle_azw3 = options.iskindle and ('MOBI' in options.format or 'EPUB' in options.format)
     options.kindle_scribe_azw3 = options.profile == 'KS' and ('MOBI' in options.format or 'EPUB' in options.format)
     checkPre(source)
     print(f"{job_progress}Preparing source images...")