gr33nhouse improvements

Improves the situation in #66, closes #73 (closed)

• Improves memory usage slightly and maybe makes larger app downloads more reliable
• Adds an error screen that exposes it when we're OOMing
• Switches downloads to /flash/apps/ from /flash/sys/apps/.
• Actually utilizes the download _try count to show an error after 3 tries.
• Display download progress
• General cleanups