work on ugoira converter
Various fixes to ugoira->webm converter

* Fix regex for getting frame data not working if agent is logged in to
pixiv
* Fix #unpack not returning the unpacked folder
* Fix frame_data being inaccessible because it was a local variable
* Fix images getting put in tmpdir, when they're expected to be in
tmpdir/images
* Fix deleting the tmpdir manually (it gets deleted automatically)
* Fix output webm being put in tmpdir (which gets deleted) instead of
write_path
Fix last frame of webms not displaying right in some browsers

Some browsers like Chrome (and some video players like MPC-HC) do not
display the last frame of a webm (or they display it, but only very
briefly) if set to loop. This commit is a hack to force the last frame
to display for the correct amount of time by duplicating it.
implement ugoira converter
integrate ugoira converted into upload flow
minor sanitization of file extensions
Fix webm converter outputting non-webm videos

mkvmerge didn't realize it was supposed to output a webm specifically
because write_path does not have a file extension. The --webm option
tells it this instead.
refactor
integrate ugoiras into zip+webm+preview
add ugoira support in view
fully implement ugoira js player, upgrade jquery and jquery-ui
Fix frame data record not being expunged along with post
Fix error reading zip
Fix zip file not being closed

file.get_input_stream leaves the file open by default, which means the
zip cannot be moved later on. But the block version of it closes the
file automatically.
Fix large webm sample writing to .jpg path
Fix argument error
Fix get_image_url_from_page call
Fix webm posts linking to nonexistent large_file_path
Fix ugoira thumbs not being scaled down to 150x150
Simplify zip extracting code