Extend GM5 plugin to support old "view" variables. Bind GM5 graphics better.

This pull request adds in support for the old GM5 view variables: view_x,view_y,view_width,view_height,view_left,view_top. These are bound (by reference) to their newer equivalents (e.g., view_xview, view_xport), so they interact seamlessly and interchangeably. Care was taken to ensure that the array access syntax works (so, view_width vs. view_width[0]). 

In addition, the "brush_color" used for drawing GM5 objects was bound to draw_get_color() and draw_set_color(). This allows more predictable interactions when old+new syntax is used in the same game.

Note that both these changes only affect the GM5 plugin, which is disabled by default.