implemented new block system

Fixes recurring design issue that the Blocks were a frequent exception to the
DAG concept. The Blocks connecting to each others inputs/outputs while not
necessarily being "dependent" on each other to produce an image continually
causes issues while trying to create a rendering code path. This redesign
should provide a more "directed" approach to the directed acyclic graph.

app/widget/timelinewidget/tool/slide.cpp

@@ -81,7 +81,7 @@ void TimelineWidget::SlideTool::InitiateGhosts(TimelineViewBlockItem *clicked_it
       AddGhostFromBlock(ghost_block->previous(), ghost->Track(), olive::timeline::kTrimOut);
     }
 
-    if (ghost_block->next() != nullptr && ghost_block->next()->type() != Block::kEnd) {
+    if (ghost_block->next() != nullptr) {
       AddGhostFromBlock(ghost_block->next(), ghost->Track(), olive::timeline::kTrimIn);
     }
   }