Point of view selector

[wafels]

Once image re-projection has been implemented, helioviewer.org should have some way of selecting the point of view from which the images are shown. This will help separate the point of view from the images. Changing the point of view will cause all the data in the viewer window to be re-projected from that point of view. In the first example, only a few different points of view will be available, for example Earth, STEREO-A/B, Parker Solar Probe, Solar Orbiter.

Note that this may require the re-calculation of some archived images, since the image data may have been corrected without the necessary changes to the image meta data.

[dgarciabriseno]

This is paired with Helioviewer-Project/api#237