0.139.2 -- I am getting better

I am finally getting better after my surgery few weeks ago, so I can work more on the game again :)

Mostly, those changes relates to the statistics system and new graph system, but there are some balancing changes and long awaited bug fixes included too.

⚖ Balance

• Make tower upgrade sellable
• Upgrades can be bought mid-run
• Mobs can be bought mid-run
• Boost arrow tower

🚀 Features

• Add little variety to road tiles
• gold graph ingame
• Statistics are persisted long term
• Mob reward graph
• Tower damage graph
• Add ambient sound and two new music tracks
• Aggregate damage numbers particles to reduce spam

🐛 Bug Fixes

• Fix tabbed view to show currently selected button
• Elapsed time is restored on statistics loading
• Reset all progress resets also saved statistics
• Actually persist gameId
• Do not give gold when mob is already dead