Add magneticVariation and magneticVariationValid property to QML Position

[ChangeLog][QtPositioning][Position] Added magneticVariation and
magneticVariationValid property to the QML Position type

Task-number: QTBUG-39547
Change-Id: I59d0039f2b501701f67404dabef2ab4c62bcb16b
Reviewed-by: Aaron McCarthy <mccarthy.aaron@gmail.com>
Fix revision and docs for new MapType::night property

This property was recently added but not properly advertised as Qt 5.4+
API element and the QML revision was not set.

Change-Id: Iab6a125269d627d5e1b3a0e457f6a42708ea7026
Reviewed-by: Aaron McCarthy <mccarthy.aaron@gmail.com>