QT_STATIC_CONST is gone with Qt 5.4


git-svn-id: svn://svn.code.sf.net/p/qwt/code/branches/qwt-6.1@2065 29e17f8d-cf37-471e-a288-72cc03a76eda
QT_STATIC_CONST_IMPL is gone since Qt 5.4


git-svn-id: svn://svn.code.sf.net/p/qwt/code/branches/qwt-6.1@2066 29e17f8d-cf37-471e-a288-72cc03a76eda