feat: refactor shared.Message to a channel

- remove `shared` package and shared.Message
- rename `notifications` package to `frontend`
- introduce a channel send the received ServerMessages to the frontend handler(s)
- move keyhandler to goroutine
- simplify password handling in Start function
- update import names when importing from GoTomoto

pkg/models/configfile.go

@@ -1,11 +1,11 @@
 package models
 
 import (
-	"git.smsvc.net/pomodoro/GoTomato/pkg/models"
+	GoTomato "git.smsvc.net/pomodoro/GoTomato/pkg/models"
 )
 
-type ConfigFile struct {
-	URL            string                        `yaml:"url"`
-	Password       string                        `yaml:"password"`
-	PomodoroConfig models.GoTomatoPomodoroConfig `yaml:"config"`
+type Config struct {
+	URL            string                          `yaml:"url"`
+	Password       string                          `yaml:"password"`
+	PomodoroConfig GoTomato.GoTomatoPomodoroConfig `yaml:"config"`
 }