fix kicker in interpolation

[rdemaria]

address #1146

[ldeniau]

There are a few flaws in this improvement.

1. [hv]kicker haven't [vh]kick attributes, and your test is using only the kick attribute when dealing with [hv]kickers and the [hv]kick attributes with kickers so it's not failing and it doesn't detect the problem.
2. [hv]kickers and kickers also have the c[hv]kick attributes which are not considered by the PR. The Correct command sets these attributes for orbit correction.
3. tkickers are not processed. BTW, tkicker have c[hv]kick attributes that are useless since they are never considered by orbit correction, and there are c[hv]flag attributes probably introduced a long time ago to consider/discard tkickers in orbit correction, but they are never used in the code.

[rdemaria]

Thanks for the comments! Ok for 2 and 3. For 1 I agree with the reasoning, but it was I implemented. The added test shows the correct behaviour!

[rdemaria]

btw c[hv]kick are part of the element dictionary, but if I understand well only the values in the nodes are used.