Ship upgrades!

Changes in latest push:

• Added more starting cash (7.5k => 20k). Right now it's too hard to make credits, will adjust sell values coming up next
• Can buy ship upgrades at the bottom of some marketplace lists
• Added basic ship upgrade screen on Shipyards which are accessible inside of planets
• Ship yards (to install upgrades) will now appear more
• Now the players inventory and ship upgrades are being persisted
• No longer sell level 1 ship upgrades. Level 1 ship upgrades were for sale even though the player has all level 1 systems to start; original reasoning for this is explained below
• Can no longer purchase duplicate ship upgrade parts. Previously, players could have purchased duplicate upgrades. The idea was to allow multiple of the same upgrade, for example cargo or fuel bays to increase a ship's ability in those areas. Will revisit this in the future I'm sure

Todo (soon):

• Still need to add some kind of basic sound effects
• Really need to balance economy, it's just not fun atm, can't make money easily enough
• Add more variety to the planet generation
• Make planet/system "Industry" matter
• Add some kind of "chat" to the planet menu to pull details out of nps, where to sell for most value or where are points of interest

Todo (far out):

• Add npc's (/enemis)
• Add some kind of derelicts (maybe missions)
• Flying is kind of fun so maybe some kind of racing system or something
• Clean up all the dirty UI
• Add some "tutorial" for new players

Yea, so this was just a quick ship-upgrade update I could manage in my spare time. I know the game isn't super fun atm so I'm going to probably do another couple passes on cleaning up/adding basic things then work on trying to get a better gameplay loop added.