Add hibernation support to avoid time shifts about time-limit

[marbetschar]

We can use a fix similar to this: elementary/greeter#472

[marbetschar]

@vjr I tried to implement your hibernation support logic into my Time Limit app, but for some reason the callback is not fired. Do you have any idea why this does not seem to work? Would be awesome if you can point me into the right direction :)

https://github.com/marbetschar/time-limit/compare/bugfix/hibernation-support

[vjr]

Hi! I'm not too familiar with this but can you try sleep (suspend to RAM) instead of hibernate (suspend to disk) and see if that works? The freedesktop docs say the PrepareForSleep signal is supposed to trigger for both modes but it's worth a try?

[marbetschar]

@vjr thanks for your quick response! I made an error and wrongly named the DBus interface org.freedesktop.login1.LoginManager instead of org.freedesktop.login1.Manager. After correcting this, your code proposal magically started to work! Thank you so much for pointing me towards to the freedesktop specs!