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