commands: Show server error info in browser

The main item in this commit is showing of errors with a file context when running `hugo server`.

This can be turned off: `hugo server --disableBrowserError` (can also be set in `config.toml`).

But to get there, the error handling in Hugo needed a revision. There are some items left TODO for commits soon to follow, most notable errors in content and config files.

Fixes #5284
Fixes #5290
See #5325
See #5324

hugolib/hugo_sites_build.go

@@ -19,8 +19,6 @@ import (
 
 	"errors"
 
-	jww "github.com/spf13/jwalterweatherman"
-
 	"github.com/fsnotify/fsnotify"
 	"github.com/gohugoio/hugo/helpers"
 )
@@ -79,7 +77,7 @@ func (h *HugoSites) Build(config BuildCfg, events ...fsnotify.Event) error {
 		h.Log.FEEDBACK.Println()
 	}
 
-	errorCount := h.Log.LogCountForLevel(jww.LevelError)
+	errorCount := h.Log.ErrorCounter.Count()
 	if errorCount > 0 {
 		return fmt.Errorf("logged %d error(s)", errorCount)
 	}