Ship stripped down version of ICU data library (icudt49.dll)

uThe icudt49.dll we ship in our binary installers is 17,5 MB big. Any developer that wants to distribute his Qt application has to include this BLOB, which lead to various complains about Qt 5 being 'too big'.

Ideally we should therefore strip down the data that we ship in the .dll. This can be done by e.g. using the ICU Data customizer: http://apps.icu-project.org/datacustom/ . Means to extend this data by e.g. replacing the icudt49.dll, or adding separate .data files , must be furthermore documented.