[FL-2556] Update complete screen (#1332)

* Desktop: slideshow implementation
* Updater: handling splashscreen installation; added format version field to slideshow binary
* Desktop: added bidirectional slideshow navigation + instant cancel by "back" button; Updater: rebalanced update stages weights
* Updater: fixed missing field init; fixed potential loop when baking slideshows
* Assets: fixed "update complete" image to match original
* Desktop: added check for slideshow file version
* Scripts: slideshow.py cleanup
* Desktop: removed first start intro sequence
* Desktop: removed first start remnants

applications/desktop/helpers/slideshow.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include <gui/canvas.h>
+
+typedef struct Slideshow Slideshow;
+
+Slideshow* slideshow_alloc();
+
+void slideshow_free(Slideshow* slideshow);
+bool slideshow_load(Slideshow* slideshow, const char* fspath);
+void slideshow_goback(Slideshow* slideshow);
+bool slideshow_advance(Slideshow* slideshow);
+void slideshow_draw(Slideshow* slideshow, Canvas* canvas, uint8_t x, uint8_t y);