The use_low_power_mode setting defaults to false
Do not install gconf schemas if builtin-gconf is in use
Do not save config keys that still have the default value

This way mce package upgrade can change config keys that the
user has not explicitly set to non-default value.
Use helper function for setting high brightness mode

If mce for some reason tries to write out of bounds data to the high
brightness mode sysfs file, it will be logged and capped to valid range.
Merge pull request #41 from spiiroin/display_lpm_config

Low power mode display is disabled by default