Create interaction (troop movement) dialog

[ultimate]

In system selection #146 buttons are shown on the left along with the system info #316.
When the button is pressed a small dialog should be shown that allows selecting the amount of of troops to be sent.

[ultimate]

Only allow interaction when user is logged in

[ultimate]

When not logged in, "send" button in system list should be hidden

[ultimate]

Implement a synced arrival (see #39, too)