Option "Start restbreak when screen is locked" doesn't work as expected

[escrevebastante]

Describe the bug
I configured workrave with the "Start restbreak when screen is locked" option enabled. However, once i lock my screen, the timer for the restbreak doesn't reset.

To Reproduce
Steps to reproduce the behavior:

1. Disable Micro-break by unchecking the box on Preferences menu: "Timers -> Micro-break -> Enable timer"
2. Enable Rest break by checking the box on Preferences menu: "Timers -> Micro-break -> Enable timer". I also have checked the box "Start restbreak when screen is locked" and unchecked the box "Enable shutting down the computer from the rest screen"
3. Other options are pretty much default

Expected behavior
Once i lock the screen, the rest break should start. Once i unlock the screen, the rest break timer should be reset. I am using "xflock4" command to lock the screen

** Linux (please complete the following information in case you encountered the bug on Linux):**

• Distribution: OpenSUSE
• Distribution Version: Tumbleweed
• Desktop Environment: XFCE 4.10
• Workrave Version 1.10.44

[rcaelers]

Workrave uses the Gnome session manager to detect the 'presence status' of the user. When the screen is locked, the presence status is set to idle. This method will work for Gnome/Cinnamon, but likely not for XFCE, MATE, KDE,... I will investigate if this can be supported for XFCE as well (or add a remark to the UI that support of this feature depends on the desktop environment)