[ground_segment] represent unconfirmed settings with infinity

proposal to fix #1012:
- server: represent initial/unknown/unconfirmed settings with infinity
- page_settings: set label text to "?" upon commit and on update if value is "inf", also set label to "?"
[cockpit] add tooltip for current settings value label
[ground_segment] settings: also set current value lable to ? when requesting update
[messages] disable message frame sensitivity during drag

- it also disable update of new message
- it can solve a bit of #966
[messages] hide notebook and display help during drag

It is an other way to solve #966 with the advantage that the "drag
route" is made easier since during drag most of the messages window is
hidden
[GCS] alert/console window: always insert messages at the end

closes #996