Clean up for v0.6.0 release

[fhagemann]

This PR does some cleanup for the v0.6.0 release.

• Obsolete functions were removed (Clean up: remove obsolete functions #87)
• Docs were added (props to @lmh91) for Grid
• Docstrings were added for exported functions
• Example config files were updated (f2d6b78) to avoid deprecation warnings
• Update get_world_limits_from_objects (de97af5)
• Functions from IntervalSets.jl: endpoints and width replaced self-written ones ( c942aa8, 22ec004, 80ce13e)
• LengthQuantity and AngleQuantity were moved from SolidStateDetectors to ConstructiveSolidGeometry (e2fc079)
• to_internal_units was changed (b24d6ed) to only expect one argument (and determine the internal unit from the argument)
• Checks were added to ensure that all input_units match what they are describing (984e8ad)
• Keywords to disable painting were added (ead7bd8)

[lmh91]

What about

    e_drift_field = get_interpolated_drift_field(s.electron_drift_field);
    h_drift_field = get_interpolated_drift_field(s.hole_drift_field);

in simulate_waveforms? These are of type ElectricField.

Ah, right. I thought, they were separate types.. Then, I'll leave it ;)

We might want to change this to VectorField (and also ScalarField for ElectricPotential, ...).
But not right now.

[fhagemann]

I would leave this PR as is and suggest one final PR before the v0.6.0 release in which we take care of code style, e.g.:

• find consistent naming for variables (detectors are c, d, ssd, det), simulation (s, sim, simulation)
• consistent naming of types (to only use CylindricalGrid{T}} or Grid{T,3,Cylindrical}} in functions, etc.)
• write one-liner in one line etc.
• consistent docstrings

[lmh91]

Sounds good.