Implement constant parameter ODE solver

[gergopokol]

Rate equations are a set of ordinary first order linear differential equations. For constant parameters it is possible to solve this analytically, offering an ideal test case. As a first step, the constant parameter version of this solver is to be implemented along with its unit tests.

[gergopokol]

@SzondyB : TestOde should be refactored following example of test_1d_analytical, and test suit should be extended for more coverage.

[gergopokol]

test_set_up_equation has ben ammended with two dummy parameters to run, but I am not at all sure why we need inputs calculation_point and steps in set_up_equation(variable_vector, calculation_point, coefficient_matrix, steps) is needed. Without is, however, the odeint solver does not run.

[asztalosors]

The input data object allocation is faulty. If different data sources are to populate the object ex: constant plasma, hdf5 plasma input, ids input, an intelligent switch has to be implemented to avoid rewriting the code.

[asztalosors]

The routine has a bug, when running "set_up_equation" in line 39 of ode.py. "derivative_vector = numpy.dot(variable_vector, interp_coefficient_matrix(actual_position))"

The error is related to the usage of the interp_coefficient_matrix function outside of the interpolation range allotted.

[asztalosors]

The temporary bug fix implemented in 36d9ef4 has to be further attended to and the actual interpolation range overflow fixed.

[asztalosors]

Preliminary beam evolution results for constant plasma .

[asztalosors]

The routines suffer from object duplication, input allocation is manually resolved, overflow errors.

[gergopokol]

Constant parameter solver is to be removed, because it there only for historical reasons.