Fix instability in RBM

[YifanCheng]

Numerical instability was found in river temperature and reservoir temperature simulation results in RBM. In this PR, the numerical instability problem is fixed. Main changes made are concluded as follows:

• Add estimation of errors caused by numerical method (river temperature and reservoir temperature)
• Set up minimum wind speed to be 1m/s
• Apply dynamic timesteps in calculating reservoir temperature based on the numerical error estimation
• Set the minimum depth to be 5 feet

[YifanCheng]

This pull request was merged as this is a stable version of RBM-2L.