Add config to disable table mode syntax

Since table mode syntax can hamper performance, it is now possible to
disable it with a global config

plugin/table-mode.vim

@@ -44,18 +44,14 @@ call s:SetGlobalOptDefault('table_mode_eval_formula_map', '<Leader>tfe')
 call s:SetGlobalOptDefault('table_mode_echo_cell_map', '<Leader>t?')
 call s:SetGlobalOptDefault('table_mode_sort_map', '<Leader>ts')
 
+call s:SetGlobalOptDefault('table_mode_syntax', 1)
+
 function! s:TableEchoCell() "{{{1
   if tablemode#table#IsRow('.')
     echomsg '$' . tablemode#spreadsheet#RowNr('.') . ',' . tablemode#spreadsheet#ColumnNr('.')
   endif
 endfunction
 
-augroup TableMode
-  au!
-
-  autocmd Syntax * if tablemode#IsActive() | call tablemode#SyntaxEnable() | endif
-augroup END
-
 " Define Commands & Mappings {{{1
 if !g:table_mode_always_active "{{{2
   exec "nnoremap <silent>" g:table_mode_map_prefix . g:table_mode_toggle_map ":<C-U>call tablemode#Toggle()<CR>"