vifm: Extend nsxiv thumbnailer

Now works recursively, only looks for fitting format extensions and can
display video thumbnails as well.

All options are documented in `-h` help display - `-r` enables recursive
lookup for directory current file is in, `-m` enables displaying video
thumbnails (takes a little longer to load) and `-t` starts nsxiv in
thumbnail mode.

vifm/.config/vifm/vifmrc

@@ -290,7 +290,8 @@ nnoremap <space>F :grep<space>
 " preview thumbnails of current folder
 " select thumbnails with m/M in nsxiv
 " to generate a filtered view on them
-nnoremap <space>t :!nsxiv -t %u -o %d<cr>
+nnoremap <space>t :!vifm-thumbnailer -t %u %c<cr>
+nnoremap <space>T :!vifm-thumbnailer -r -t %u %c<cr>
 
 " allows preview to work for normal view and single pane view
 noremap <silent> w : if &quickview && !layoutis('only')
@@ -318,7 +319,7 @@ set classify+=' ::*.bmp,,*.gif,,*.jpeg,,*.jpg,,*.ico,,*.png,,*.ppm,,*.svg,,*.
 " audio
 set classify+=' ::*.aac,,*.anx,,*.asf,,*.au,,*.axa,,*.flac,,*.m2a,,*.m4a,,*.mid,,*.midi,,*.mp3,,*.mpc,,*.oga,,*.ogg,,*.ogx,,*.ra,,*.ram,,*.rm,,*.spx,,*.wav,,*.wma,,*.ac3::'
 " media
-set classify+=' ::*.avi,,*.ts,,*.axv,,*.divx,,*.m2v,,*.m4p,,*.m4v,,.mka,,*.mkv,,*.mov,,*.mp4,,*.flv,,*.mp4v,,*.mpeg,,*.mpg,,*.nuv,,*.ogv,,*.pbm,,*.pgm,,*.qt,,*.vob,,*.wmv,,*.xvid::'
+set classify+=' ::*.avi,,*.ts,,*.axv,,*.divx,,*.m2v,,*.m4p,,*.m4v,,*.mka,,*.mkv,,*.mov,,*.mp4,,*.flv,,*.mp4v,,*.mpeg,,*.mpg,,*.nuv,,*.ogv,,*.pbm,,*.pgm,,*.qt,,*.vob,,*.wmv,,*.xvid::'
 " office files
 set classify+=' ::*.doc,,*.docx::, ::*.xls,,*.xls[mx]::, ::*.pptx,,*.ppt::'
 
@@ -433,6 +434,8 @@ fileviewer *.gif
 
 " Images
 filextype *.bmp,*.jpg,*.jpeg,*.png,*.gif,*.xpm
+        \ {View in nsxiv directory viewer}
+        \ vifm-thumbnailer %c,
         \ {View in nsxiv}
         \ nsxiv %f,
         \ {View in vimiv}