Improve clarity in parameter attribute names

[BDonnot]

Some attributes names in the Parameters are obscure, for example NB_TIMESTEP_POWERFLOW_ALLOWED which should be NB_TIMESTEP_OVERFLOW_ALLOWED.

We can also improve names of the NB_TIMESTEP_TOPOLOGY_REMODIF and NB_TIMESTEP_LINE_STATUS_REMODIF to match the "cooldown" terminology adopted in observation for example.

To this regard, observation attribute time_before_cooldown_line and time_before_cooldown_sub are not that clear.

Also NB_TIMESTEP_RECONNECTION means something like "number of time step i have to wait if i disconnect a powerline that has been deconnected because of an overflow". The name is not clear.

[BDonnot]

This has been improved in 0.9.0