Fixes: ensure same order of units in whole Calligra UI, have ruler and page layout dialog update to change of document's unit type

also tune KoUnit API a little:
* rename KoUnit::unit(...) to KoUnit::fromSymbol(...)   <- more Qt'ish
* turn static KoUnit::unitName(KoUnit) into member method KoUnit::symbol()   <- as typical use-case is on existing KoUnit instance, also shorter and more OOed
* rename KoUnit::Unit to KoUnit::Type    <- "type" feels a better term here
* added KoUnit::type() and KoUnit::setFactor(...)    <- useful in a few places
* remove KoUnit::unitDescription(...) from API    <- not used outside
* rename KoUnit::PixelVisibility to KoUnit:: ListOption  <- more general, some might want to add other flags like HideImperial

And adds unit tests for the touched KoUnit API

Thanks to boemann and Cyrille for making it compile with Qt 4.7 as well

REVIEW: 104626