QtCreator IDE integration.

First version of QtCreator IDE integration :
'make qtcreator-ide-integration' generates .pro and .pro.user files for each subfolder of LibreOffice.
It also creates a 'lo.pro' meta project that list all other .pro files.
Developers can use use QtCreator to edit, compile and debug LibreOffice.

Change-Id: Ib05d8c36a7ca055ecd7a4db5776f4c28bf05676c
Reviewed-on: https://gerrit.libreoffice.org/15804Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>

Makefile.in

@@ -370,7 +370,8 @@ $(foreach ide,\
 	vs2012 \
 	vs2013 \
 	vim \
-	xcode, \
+	xcode \
+	qtcreator,\
 $(eval $(call gb_Top_GbuildToIdeIntegration,$(ide))))
 
 endif # MAKE_RESTARTS