[Annotations] Highlight independent variables and equation parameters for function parameters

[pafonta]

Example with parameter ID 71233092-eb80-11e5-a9b7-64006a4c56ef.

In the equation text edit, the following terms in bold could be highlighted:

1/(1+exp((potential_membrane - mid_amp_inact)/slope_factor_inact))

but differently as potential_membrane is an independent variable and mid_amp_inact and slope_factor_inact are equation parameters.