displaymanager: Make the settings follow the naming convention.

Make the defaultDesktopEnvironment and desktopFile settings in
displaymanager.conf follow the naming convention used in the other .conf
files.

src/modules/displaymanager/displaymanager.conf

@@ -12,9 +12,9 @@ displaymanagers:
   - kdm
 
 #Enable the following settings to force a desktop environment in your displaymanager configuration file:
-#default_desktop_environment:
+#defaultDesktopEnvironment:
 #    executable: "startkde"
-#    desktop_file: "plasma"
+#    desktopFile: "plasma"
 
 #If true, try to ensure that the user, group, /var directory etc. for the
 #display manager are set up correctly. This is normally done by the distribution

src/modules/displaymanager/main.py

@@ -212,8 +212,8 @@ def run():
     root_mount_point = libcalamares.globalstorage.value("rootMountPoint")
     
     if "default_desktop_environment" in libcalamares.job.configuration:
-        entry = libcalamares.job.configuration["default_desktop_environment"]
-        default_desktop_environment = DesktopEnvironment(entry["executable"], entry["desktop_file"])
+        entry = libcalamares.job.configuration["defaultDesktopEnvironment"]
+        default_desktop_environment = DesktopEnvironment(entry["executable"], entry["desktopFile"])
     else:
         default_desktop_environment = find_desktop_environment(root_mount_point)