Fixes issues with colour drop down.
Started adding init_viewport
Fix compile error
Finished viewport_create for window_ride
Use new ride window when clicking on ride
Move cursor location fix #476
#479
Fix errors/warnings in VS build

* Added libspeex to 'Debug' target, previously only 'Release' had it.
* Initialize some pointers with NULL when an uninitialized code path is
unlikely, but possible.
implement window_dropdown_show_colour
Basic analysis of window_map_mousedown

* This function doesn't appear to relevant for the normal map window, as
it doesn't have the required widgets. Considering that the Scenario
Editor has a more complex map window, I assume that this function does
processing referred to that instance instead.