Manually position updates

[TheCataliasTNT2k]

Would be great, if you can disable position updates, so you can use the map to find a group while it is not moving.
To archive this, it would be cool, to implement link specific options (to be able to change the options for each link separately without restarting the share, see #182 ).
When you disable active tracking for all links (via main menu or via link options), the device should no longer send position updates to the server.
There should also be a button in the link options, to send a position update manually. This would be very useful for groups, which do not move, without sending "phantom positions" caused by jumping GPS positions (e.g. inside buildings).
And you would be able to pause the tracking for a time, without invalidating the link.