Currently, if there are any other apps installed that can open .kra files, and they
have the `InitialPreference` value set in their .desktop file, they will open .kra
files by default instead of Krita. This is non-ideal.
This patch sets the `InitialPreference` value in Krita's own .desktop file high
enough that it will always be the default first hamdler for .kra files.
CCBUG: 337272