Revert "Revert "nvim: Switch to signify""

This reverts commit 79be97c081.

While signify has the below issue
https://github.com/mhinz/vim-signify/issues/345

still drop gitgutter and use signify as gitgutter might have problems as
observed in this thread.
https://github.com/nvim-lua/completion-nvim/issues/203

nvim/.config/nvim/after/plugin/gitgutter.vim

@@ -1,11 +0,0 @@
-nnoremap ]c :GitGutterNextHunk<CR>
-nnoremap [c :GitGutterPrevHunk<CR>
-nnoremap ghs :GitGutterStageHunk<CR>
-nnoremap ghu :GitGutterUndoHunk<CR>
-nnoremap ghp :GitGutterPreviewHunk<CR>
-nnoremap ghq :GitGutterQuickFix<CR>
-nnoremap ghf :GitGutterFold<CR>
-omap ih <Plug>(GitGutterTextObjectInnerPending)
-omap ah <Plug>(GitGutterTextObjectOuterPending)
-xmap ih <Plug>(GitGutterTextObjectInnerVisual)
-xmap ah <Plug>(GitGutterTextObjectOuterVisual)

nvim/.config/nvim/after/plugin/signify.vim

@@ -0,0 +1,10 @@
+nnoremap ghu :SignifyHunkUndo<CR>
+nnoremap ghp :SignifyHunkDiff<CR>
+nmap ]c <Plug>(signify-next-hunk)
+nmap [c <Plug>(signify-prev-hunk)
+nmap ]C 9999]c
+nmap [C 9999[c
+omap ih <Plug>(signify-motion-inner-pending)
+xmap ih <Plug>(signify-motion-inner-visual)
+omap ah <Plug>(signify-motion-outer-pending)
+xmap ah <Plug>(signify-motion-outer-visual)

nvim/.config/nvim/init.vim

@@ -20,7 +20,7 @@ Plug 'tmux-plugins/vim-tmux-focus-events'
 " Git support
 Plug 'rhysd/git-messenger.vim'
 Plug 'tpope/vim-fugitive'
-Plug 'airblade/vim-gitgutter'
+Plug 'mhinz/vim-signify'
 Plug 'rhysd/conflict-marker.vim'
 Plug 'salcode/vim-interactive-rebase-reverse'
 Plug 'stsewd/fzf-checkout.vim'

nvim/.config/nvim/plugin_settings.vim

@@ -1,15 +1,3 @@
-" Let vim-gitgutter do its thing on large files
-let g:gitgutter_max_signs=1000
-let g:gitgutter_map_keys = 0
-let g:gitgutter_highlight_linenrs = 1
-let g:gitgutter_preview_win_floating = 1
-let g:gitgutter_use_location_list = 0
-let g:gitgutter_sign_added = '+a'
-let g:gitgutter_sign_modified = '+m'
-let g:gitgutter_sign_removed = '-r'
-let g:gitgutter_sign_removed_first_line = '^^'
-let g:gitgutter_sign_modified_removed = 'mr'
-
 " Automatically detect style file and apply style to formatting
 let g:clang_format#detect_style_file = 1
 " For workspace