Allow for multiple show photo sizes, and resize on upload

[markspolakovs]

Note that this changes the config variable $default_show_url to $default_show_image_path, and will need to be updated in prod to match.

Untested, do not merge.

[mstratford]

Looks overall very good, one thing I may have either misunderstood or caught, the default show image is presumably the "Jukebox" show image, whereas I expect that's not what you want the default show image to be. Hence probably why the default show image was set to the default person one, since that's a more general URY logo and Twitter.

[mstratford]

Also wondering, this presumably doesn't yet change the option for podcast image to be "podcast_small" yet? Also, can't remember, do seasons need the show image function changing, or is that just use the show image directly?

[markspolakovs]

@mstratford good point on the jukebox one, have to check that. Re seasons, iirc seasons inherit from shows (which is kinda dumb but okay) so they should use the show's method, although I need to double-czech. Either way, I can't think of all that many places where we use season photos, usually it's either show or timeslot.

[mstratford]

Oh yeah, Indeed, we had season pages in 2013-site, but they were just dumb, so we removed them in favour of the column thing on the show page.