nvim: Replace nerdtree with vifm

Simple, experimental replacement for now. Tries to keep the previous key
functionality intact:
use <leader>e to open working directory in vifm, <leader>E to open the
directory of the current file.

Some problems will remain - currently it is hard to navigate away from
an open vifm instance with C-hjkl since it is not recognized as a vim
window anymore.

Additionally, invoking vim functions does not work from the vifm window,
which means that if I start nvim pointing to a directory, i.e. with vifm
open, it not possible for me currently to directly start up fzf to open
another file, or a buffer from the history, or similar.

nvim/.config/nvim/plugin/nerdtree.vim

@@ -1,19 +0,0 @@
-" PLUGIN: NERDTree
-" " Ecosystem
-" " Plug 'tpope/vim-fugitive' - Will have to take a closer look some other time
-" highlight the line the cursor is on
-let NERDTreeHighlightCursorline = 1
-" remove Press ? for help
-let NERDTreeMinimalUI=1
-" loads nerdtree plugin when starting vim with a directory
-" this is necessary when we lazyload nerdtree with vimplug above
-" since it would only get loaded with nttoggle otherwise, and run netrw
-augroup nerd_loader
-  autocmd!
-  autocmd VimEnter * silent! autocmd! FileExplorer
-  autocmd BufEnter,BufNew *
-        \  if isdirectory(expand('<amatch>'))
-        \|   call plug#load('nerdtree')
-        \|   execute 'autocmd! nerd_loader'
-        \| endif
-augroup END

nvim/.config/nvim/plugin/vifm.vim

@@ -0,0 +1,4 @@
+let g:loaded_netrw       = 1
+let g:loaded_netrwPlugin = 1
+let g:vifm_replace_netrw = 1
+let g:vifm_exec_args = '-c "set vifminfo=''''" -c "set statusline=''''" -c "only"'