QuietHours: added option for specifying week days
Allows more flexibility for people that work on different days than
Monday to Friday
QuietHours: small adjustments related to week days option
QuietHours: use dedicated preference file for quiet hours
Sometimes we only need to read QH preferences. Loading ledcontrol
preference file just because of that could be overkill.
This optimization is a prerequisite for one of the future features
Lockscreen: several optimizations
- Preferences get reloaded only when changed
- Hook glowpad class methods only once

Revised by bgcngm:
- Don't show blank image after boot when 'Last screen' feature is enabled
(show the last stored screen image instead), by waiting for user to be present
- Handle KeyguardImageService.ACTION_KEYGUARD_IMAGE_UPDATED intent on the newly
created broadcast receiver
QuietHours: added option for muting system sounds
Allows muting following system sounds during quiet hours:
- dialpad tones
- touch sounds
- screen lock sound
- volume adjust sound
- GravityBox charger sounds

Inspired by SlimKat

Revised by bgcngm:
- Adjusted ModPhone for compatibility with SDK 17