Combine multiple upload jobs into a single KCompositeJob so only 1 notification will be shown

Summary:
Combine multiple upload jobs for files into a single KCompositeJob so only 1 notification will be shown
Includes changes introduced in D16279

Test Plan:

1. Share of multiple files is performed using 1 composite job
   
   Setup:
   • Select multiple (big) files in dolphin and share with an Android device Result:
   • The files will be transferred using 1 CompositeUploadJob and showing only 1 notification

2. Share of file while another share is already running adds job to existing composite job
   
   Setup:
   • Select multiple (big) files in dolphin and share with an Android device
   • Share an additional file with the same Android device Result:
   • The files are all transferred using 1 CompositeUploadJob and showing only 1 notification
   • The notification is updated after adding the last file

3. Other packets are transmitted as usual
   
   Setup:
   • • Setup sharing desktop notification with device
   • Share a big file with an Android device
   • Generate a desktop notification (eg. sending or receiving an email)
     
     Result:
   • Notification packet is send immediately

Reviewers: KDE Connect, nicolasfella, albertvaka

Reviewed By: KDE Connect, albertvaka

Subscribers: albertvaka, apol, nicolasfella, broulik, kdeconnect

Tags: KDE Connect

Differential Revision: https://phabricator.kde.org/D17081