skin_engine: New tag to draw a rectangle (optionally with a gradient)

%dr(x, y, width, height, [colour1[, colour2]]):
x,y - viewport relative pixel coordinates to start the rectangle.
width, height - obvious. can be '-' to fill the viewport
if both colours are left out the viewports foreground colour will be used
if one colour is specified it will fill the rectangle that colour.
if both colours are specified it will gradient fill the rectangle.

Change-Id: Iad451e99ded663bc7c5d182443659db7d909b388

lib/skin_parser/tag_table.c

@@ -244,6 +244,7 @@ static const struct tag_info legal_tags[] =
     { SKIN_TOKEN_VAR_TIMEOUT,           "vl",   "S|D", SKIN_REFRESH_DYNAMIC },
 
     { SKIN_TOKEN_SUBSTRING,             "ss",   "IiT|s", SKIN_REFRESH_DYNAMIC },
+    { SKIN_TOKEN_DRAWRECTANGLE,         "dr",   "IIii|ss", SKIN_REFRESH_STATIC },
     { SKIN_TOKEN_UNKNOWN,                ""   , "", 0 }
     /* Keep this here to mark the end of the table */
 };

lib/skin_parser/tag_table.h

@@ -288,6 +288,8 @@ enum skin_token_type {
     SKIN_TOKEN_VAR_TIMEOUT,
 
     SKIN_TOKEN_SUBSTRING,
+
+    SKIN_TOKEN_DRAWRECTANGLE,
 };
 
 /*