Improve alignment display

[OlivierHnt]

This PR improves the alignment display when working with arrays of Complex{<:Interval}.
Somehow when the imaginary part contains a negative sign, the alignment is off.
To fix it when the imaginary part is an interval only containing negative values, the sign can be taken outside of the displayed interval.

E.g. before this PR:

julia> [1.2 - im * interval(1e-77, 1e-75) ; interval(0.1) ; interval(-0.1) ; 1.2 + im*interval(1e-77, 1e-75)]
4-element Vector{Complex{Interval{Float64}}}:
 [1.19999, 1.20001]_com_NG + ([-1.00001e-75, -0.999999e-77]_com_NG)im
                   [0.0999999, 0.100001]_com + ([0.0, 0.0]_com)im
                 [-0.100001, -0.0999999]_com + ([0.0, 0.0]_com)im
                   [1.19999, 1.20001]_com_NG + ([0.999999e-77, 1.00001e-75]_com_NG)im

after this PR:

4-element Vector{Complex{Interval{Float64}}}:
   [1.19999, 1.20001]_com_NG - im*[0.999999e-77, 1.00001e-75]_com_NG
   [0.0999999, 0.100001]_com + im*[0.0, 0.0]_com
 [-0.100001, -0.0999999]_com + im*[0.0, 0.0]_com
   [1.19999, 1.20001]_com_NG + im*[0.999999e-77, 1.00001e-75]_com_NG

The issue remains if the imaginary part is an interval containing both positive and negative values.