Standardize fieldnames across different microbe types

[mastrof]

Fieldnames of distinct microbe types should be standardized as much as possible, despite them having possibly slightly different physical meanings, e.g.:

• BrownBerg and Brumley have a motor_gain field, while in Celani the equivalent field is just called gain
• BrownBerg and Brumley have an adaptation_time field, while the Celani equivalent is called memory
• the state field in Celani is a vector, whereas it is a scalar in BrownBerg, Brumley and Xie; it's maybe more convenient to keep it a scalar and rename the internal markovian variables to something different