add_hips: Create an ImageSurvey/Image object and allow to set its opacity, colormap, ...

[ManonMarchand]

Openend this issue from the last point of #45

[ManonMarchand]

To implement this:

• create python obfject for hips with all options (dataclass?)
• or see if this could be generic (no code duplication)

[bmatthieu3]

See this JS HiPS instanciation method imageHiPS

[bmatthieu3]

I guess that for starting we do not need to have an object, just a

aladin.add_hips(url/id, options)

is sufficient to begin. It will not be possible to remove the newly added HiPS. For that we could impl something similar than for overlays described in #78
It is also possible to remove the HiPS/overlays from the UI

[bmatthieu3]

We could deprecate these Aladin properties: overlay_survey and overlay_survey_opacity