Refactor the ICU code for QLocale

Refactor the ICU code for QLocale

Clean up the ICU code and make it thread-safe. Add a
QIcuData structure to QLocalePrivate, that contains
ICU specific data.

Link against ICU directly, greatly simplifying the
code.

Also fix a bug in the locale specific case conversion
code that would cause it to fail and fall back to the
QString code if the output string was larger than the
input.

Change-Id: Ie67e5ea14fa204ebc5887d7aaeb1a4f3ecaf8697
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>