Display current stopwatch in navbar (#14122)

* add notification about running stopwatch to header

* serialize seconds, duration in stopwatches api

* ajax update stopwatch

i should get my testenv working locally...

* new variant: hover dialog

* noscript compatibility

* js: live-update stopwatch time

* js live update robustness

modules/structs/issue_stopwatch.go

@@ -12,6 +12,8 @@ import (
 type StopWatch struct {
 	// swagger:strfmt date-time
 	Created       time.Time `json:"created"`
+	Seconds       int64     `json:"seconds"`
+	Duration      string    `json:"duration"`
 	IssueIndex    int64     `json:"issue_index"`
 	IssueTitle    string    `json:"issue_title"`
 	RepoOwnerName string    `json:"repo_owner_name"`