Raise remote input timeout to 300 seconds

[ferdnyc]

The first input event on reconnection is currently being lost, this should make reconnections much less frequent. See #1836.

I don't want to mark that issue as fixed with this, since it's really just a workaround until we can figure out why input events are being lost. See my comment on the issue for more detail(/confused ramblings).

[andyholmes]

If the Closed signal works properly, you can probably remove the timeout altogether. I don't recall why I did that, it was quite some time ago now.

[ferdnyc]

@andyholmes I think we'd want to have some kind of timeout, because AFAICT Mutter doesn't have one, and is happy to leave us connected indefinitely. And there doesn't seem to be any message sent from KDE Connect that would signal the end of an input session (when the user exits the "Presentation remote" or "Remote input" interfaces, for example).

So without a timeout it seems like GSConnect would just sit around being connected... forever. Which I'm concerned could interfere with powersave and the like. (Though it's probably the other way around, entering powersave would probably forcibly disconnect us.)