[Issue-126] fix several issues with animate

[jcao-bdai]

Fix several issues related to #126

• expose "ax" and "dims" arguments to animate(...), to be consistent with other API's;
• update animate implementation to be consistent with trajectory frame's data type, in particular, SE3Array / SO3Array types instead of SE3 / SO3, in line with animate.run(...)'s implementation.

Example use-cases:

...
ax = fig.add_subplot(111, projection='3d')
T1.plot(ax=ax, dims=[-5, 10])
T1.animate(start=T2, ax=ax)  # would use the existing ax which is [-5, 10]
# T1.animate(start=T2, ax=ax, dims=[-10, 10])  # would use the existing ax and override its lims to [-10, 10]
plt.show()

[bhung-bdai]

Seems like a reasonable change to me, but I'm not a primary user of the Spatialmath animation tool. I would feel more comfortable if there was infra to unit test, but I'm also not Spatialmath comes with that in the first place.

[myeatman-bdai]

Approved, minor comment.

[myeatman-bdai]

should we have a runtime error that check's for length 2 or 6?

[jcao-bdai]

thanks! added this check in 27fd4aa