Rock venting fix, easier tank expand/collapse

Fixed that asteroids wouldn't increase their total space when venting rock, which was preventing tank compression
(L40 in updated USI_AsteroidTank.cs)

Added buttons to let users change the rate of tank expansion/compression/dumping, making it easier to manage tanks with potentially millions of units
(L72-91/L108/L171/L178/L182 in updated USI_DynamicPort.cs)

Current step size is now displayed on the right-click menu for attachable tanks
(L95 in updated USI_DynamicPort.cs)

Compress/dump button text made consistent with expand button text
(L34/L53 in updated USI_DynamicPort.cs)