Multiple improvements to build process

Restructure and document retroshare.pri variables and helper functions
Link sqlite statically like other libraries on Android
qmake has multiple win32-* specs match them correctly
Move a buch of generic thing to retroshare.pri instead of having them replocated
  accross project specific .pro
Fix retroshare-gui too many symbols exported on windows liking error by adding
  QMAKE_LFLAGS+=-Wl,--exclude-libs,ALL
Rename retroshare-gui/src/util/win32.h because the name is too prone to
  confusion and build conflicts
libreasapi avoid usage of cretar_prl link_prl that seems unreliable on some
  platforms
libreasapi rename LIBRESAPI_QT to more understendable LIBRESAPI_SETTINGS
Use use_*.pri instead of copy pasting error prone qmake snippets around
Expose bitdht option to retroshare.pri
Add RS_THREAD_LIB qmake variable for better crossplatform support
Move debug and profiling generic options to retroshare.pri (avoid copy/pasting)
Remove Qt script module in qmake as it is not available anymore

openpgpsdk/src/use_openpgpsdk.pri

@@ -0,0 +1,20 @@
+DEPENDPATH *= $$system_path($$clean_path($${PWD}/../../openpgpsdk/src))
+INCLUDEPATH  *= $$system_path($$clean_path($${PWD}/../../openpgpsdk/src))
+LIBS *= -L$$system_path($$clean_path($${OUT_PWD}/../../openpgpsdk/src/lib/)) -lops
+
+!equals(TARGET, ops):PRE_TARGETDEPS *= $$system_path($$clean_path($${OUT_PWD}/../../openpgpsdk/src/lib/libops.a))
+
+sLibs =
+mLibs = ssl crypto z bz2
+dLibs =
+
+static {
+    sLibs *= $$mLibs
+} else {
+    dLibs *= $$mLibs
+}
+
+LIBS += $$linkStaticLibs(sLibs)
+PRE_TARGETDEPS += $$pretargetStaticLibs(sLibs)
+
+LIBS += $$linkDynamicLibs(dLibs)