Remove the ‘text’ variable from the code for the ‘say’ instruction

We only use it in one place as a substitute for ‘arguments.content’ so
if we just use the latter we can get rid of the variable.
Fix a bug when using named colors in dialog scripts

Trying to write something like

    Lobby = Character { name="Lobby", textColor=Color.Black }

would crash the game because LNVL would not recognize ‘Color.Black’.
More specifically, the if-else branch in Graphics.DrawText() would
fail to recognize the color (i.e. a table) as a valid color because
that function checks metatables to determine what a table represents.
This patch makes ‘Color’ the metatable of every named color available
so that DrawText() and similar functions can recognize such tables as
colors by checking for that metatable.