Fix various GUI issues

[nagmat84]

This PR fixes various GUI which @kamil4 discovered during his tests of #323 (see #323 (comment)), but which already affect the current master. I hope I fixed all of them without breaking anything else. 🙈

I also hijacked @ildyria PR LycheeOrg/Lychee#1578 for the backend to sync these fixes. Hence, you can simply checkout LycheeOrg/Lychee#1578 to test the changes.

@kamil4 wrote in #323 (comment)

Uploading to the root album (albums view) doesn't work for an admin for me (weirdly, it seems to pass an ID of one of the tag albums in the Photo:add request?!). Unusually, it works for non-admin users.

Should be fixed by aaa6f38. While the fix itself seems to be easy, I added a lot of comments to warn about the fragility of the code.

Album owners don't get to see the "Share" button in the header until the album is made public and the "Share button is visible" is checked.

Should be fixed by 1286b08. This bug seems to be around for a very long time now. I don't have any non-admin users for my gallery and even if I had I assume I would not have noticed that bug.

When the album is made public and the "Share button is visible" is checked, going (as an authenticated owner) to one of the photos inside the album and opening the visibility dialog is supposed to display read-only visibility status, in this case including a checked "Share button is visible". But that button is not checked.

Should be fixed by 0e02359. This one was a silly oversight when migrating to the new modal dialog.

[ildyria]

LGTM.