Moved type enum out of GLWTWindowEvent

this helps keeping syntax consistent between C and
C++ otherwise all uses of the enum constants
have to be preposed by GLWTWindowEvent::
Merge branch 'master' of https://github.com/progschj/glwt
Revert "Moved type enum out of GLWTWindowEvent"

This reverts commit 059d9b36346dcff1ef667aeb03abd876d71a76fa.