[tracker] Don't query Tracker for values it doesn't support
[tests] Add test case for FSStoragePlugin::getChildPropertyValues()
specfile
debug & callgrind
property debug
[propertypod] convert if-else if in constructor to switch statement

Results in less cluttered code.
Taken advantage of implicit type conversions to QVariant.
Ordered cases by MTP_DEV_PROPERTY value.
[deviceinfo] refactor DeviceInfo::getBatteryLevelForm()

Method now returns a QVariant holding either MtpRangeForm or MtpEnumForm
structure depending on the actual format of the device property.

Its test case updated accordingly.
Rename getBatteryLevelForm() -> batteryLevelForm()

Name now conforms with Qt coding standards for getters.
Reformat PropertyPod::getDevicePropDesc()

Less code nesting.
Utilize implicit conversions to QVariant.
Ordered cases by MTP_DEV_PROPERTY value.
[deviceinfo] add support for reporting BatteryLevel (0x5001)
Added a note about misleading MTP 1.1 device properties specification