Improve photo layout performance

[nagmat84]

While I have been working on some other PRs I noticed that some bottle necks in the layout routine for albums:

• When we rearrange the photos of the layout, the layout should be hidden such that each relayouted child triggers a re-drawing
• Stop querying the DOM for CSS selectors several times
• When the DOM has been manipulated (i.e. the photos have been added), we must provide the engine a time slice to catch up with the new DOM otherwise querying CSS attributes is slow (--> make justify asynchronous, wrap it into setTimeout).

[kamil4]

Looks mostly good to me (untested) but I did have a few questions/comments.

[nagmat84]

I had to revert one change in c6bcfac. I also added a (long) comment what the problem is so that I (or someone else) remembers and understands what the root cause is.

[kamil4]

I played with it around a bit and didn't spot any problems.