Isolation of windows headers using prewin.h
and postwin.h headers and making headers
dependent on them more self contained.

Conversion of TCHAR to WCHAR and
LPCTSTR to LPCWSTR etc. and cleanup
of unnecessary casts.

Change-Id: I7eff5c477d9223a064bfb4d962ff6d61960ee69c
Reviewed-on: https://gerrit.libreoffice.org/19901Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>