Upgradable Vehicle Depot

Inspired by Ravinus' vehicle depot (https://hub.coigame.com/Blueprint/Detail/213), however I've condensed it a little and removed storage I didn't want. In turn, I made it upgradable from T1 to T3.

Little changes needed:

• T1 to T2: After upgrading assembly II to assembly III, change both the recipe for mechanical parts to use steel and the providing unit storage to store steel.
• T2 to T3
  • Delete the last two tiles of all transport connecting to the old T2 depot
  • Remove the old T2 depot

The pipe in the T1 and T2 blueprints marks the T3's keep clear area.