[UX] Play button/action should not pause

Currently, the Play action will also pause playback, which is not in the sense of the Play action (see http://forum.xbmc.org/showthread.php?tid=203347 which I have to agree). If a user want's to have the PlayPause behavior mapped to a key/button, then he should use the PlayPause action instead - that's what we have it for. With PR #5244 I already changed the existing keymaps to use the PlayPause action for play_pause keys in our keymaps - so this change should be save to do and not change behavior for correctly done keymaps.

@MilhouseVH mind adding this to the OE testbuilds to get feedback?
@FernetMenta please check if my change to the pause action handling makes sense (always set playspeed to default)
@jmarshallnz please also have a look if you find the time