Debian package builder (#876)

* Add debian build files
* Add debian package build code to setup script
* Update the licenses in debian/copyright
* Fix a typo in windows setup docs
* Remove duplicate files
* Add missing fallback icons to assets

.gitignore

@@ -1,13 +1,14 @@
 # Setup/Install
 /MANIFEST
-/dist/
 /build/
 /deploy/
+/dist/
+/dist_deb/
 *.spec
 *.egg-info
 setup.iss
-novelwriter.desktop
-novelWriter.pyw
+/novelwriter.desktop
+/novelWriter.pyw
 
 # Translations
 /novelwriter/assets/i18n/*.qm