ADD: pixmaps.txt: New file types: Lua script (lua), presentations (odp, ppt, pptx) (#292)

pixmaps.txt

@@ -9,13 +9,17 @@ iso=application-x-cd-image
 jpeg=image-x-generic
 jpg=image-x-generic
 log=text-x-log
+lua=text-x-lua
 mp2=audio-x-generic
 mp3=audio-x-generic
+odp=x-office-presentation
 ods=x-office-spreadsheet
 odt=x-office-document
 pas=text-x-pascal
 pdf=application-pdf
 po=text-x-po
+ppt=x-office-presentation
+pptx=x-office-presentation
 rpm=application-x-rpm
 sh=application-x-shellscript
 txt=text-x-generic