* Fix pdf and plain text previws in lf
Pdf previws don't appear because are generated with wrong filename.
Plain text previws with `bat` don't respect terminal theme and have
annoying border.
* Revert pdf cache filename to work properly
fallback to using mediainfo when ffmpegthumbnailer or pdftoppm is not available.
correct terminal width for bat.
use cut instead of awk for efficiency.
improve spacing/indentation for the sake of consistency in code.
