KFormat - Add new KFormat class

KLocale offers a number of extra formatting options not yet available
in Qt. The KFormat class adds these options to KCoreAddons:

* formatByteSize()
* formatDuration()
* formatDecimalDuration()
* formatSpelloutDuration()
* formatRelativeDate()
* formatRelativeDateTime()

The KFormat class can be initialised with any QLocale to use in the
date and number formatting, or the default locale can be easily
accessed via KFormat():

QString result = KFormat().formatDuration(1000);