Bring most mimetypes in line with XDG specifications. The following are not fully verified in source as of this commit due to ubiquity: html, empty, info, make, man, misc, source, unknown

data/desktop/x-rosegarden-device.desktop

@@ -2,7 +2,7 @@
 Comment=Rosegarden device file
 Comment[fr]=Fichier de description de peripherique Rosegarden
 Hidden=false
-Icon=midi
+Icon=audio-midi
 MimeType=audio/x-rosegarden-device
 Patterns=*.rgd;*.RGD
 Type=MimeType

data/desktop/x-rosegarden21.desktop

@@ -2,7 +2,7 @@
 Comment=Rosegarden 2.1 file
 Comment[fr]=Fichier Rosegarden 2.1
 Hidden=false
-Icon=midi
+Icon=audio-midi
 MimeType=audio/x-rosegarden21
 Patterns=*.rose
 Type=MimeType

data/desktop/x-soundfont.desktop

@@ -2,7 +2,7 @@
 Comment=Soundfont
 Comment[fr]=Echantillons
 Hidden=false
-Icon=sound
+Icon=audio-x-generic
 MimeType=audio/x-soundfont
 Patterns=*.sf2;*.SF2
 Type=MimeType