make recovery UI images more general; allow for installation animation

Change some of the UI parameters (# of indeterminate progress bar
frames, fps, etc.) from #defined constants to variables that can be
set by the device-specific recovery_ui code (via a new function).

Support overlaying different images on top of the base installation
icon to animate it.  Make the FPS control more accurate.

Change-Id: I9268b389b7ea6b3ed9e0c7eae37baf4272e60edd
diff --git a/minui/resources.c b/minui/resources.c
index 3d2c727..2170dca 100644
--- a/minui/resources.c
+++ b/minui/resources.c
@@ -49,6 +49,8 @@
     png_structp png_ptr = NULL;
     png_infop info_ptr = NULL;
 
+    *pSurface = NULL;
+
     snprintf(resPath, sizeof(resPath)-1, "/res/images/%s.png", name);
     resPath[sizeof(resPath)-1] = '\0';
     FILE* fp = fopen(resPath, "rb");