Change some diagnostics defaults

When loading diagnostics:
  * Disable underlining.  It is uncomfortable to have all the syntax
    highlighting changed because of the underline effect.
  * Also advice on diagnostics while typing (Insert Mode).
  * Show diagnostics menu on hold but only when editing, otherwise there
    is a keybinding available.

nvim/language_server.vim

@@ -39,9 +39,13 @@ lua << EOF
 local nvim_lsp = require('lspconfig')
 
 local on_attach = function(client, bufnr)
-  vim.api.nvim_command('autocmd CursorHold <buffer> lua vim.lsp.diagnostic.show_line_diagnostics()')
+  vim.api.nvim_command('autocmd CursorHoldI <buffer> lua vim.lsp.diagnostic.show_line_diagnostics({show_header = false})')
   vim.lsp.handlers["textDocument/publishDiagnostics"] = vim.lsp.with(
-      vim.lsp.diagnostic.on_publish_diagnostics, {virtual_text=false}
+      vim.lsp.diagnostic.on_publish_diagnostics, {
+        update_in_insert = true,
+        underline = false,
+        virtual_text = false
+      }
   )
   require('compe').setup({autocomplete=true}, 0)
   lsp_mappings()