ChatControl infobar: Set ellipsizing for labels and add line breaks

For file transfer related infos and for group chat invitations, an Infobar is shown in the ChatControl (label + buttons).

This adds ellipsizing to the message label, otherwise it would stretch so that the buttons are out of view.

Additionally, I added line breaks to all messages where appropriate. I also adjusted the button's labels.

Note: Adding word wrap would cause the ChatControl to stretch endlessly in vertical direction (it seems to assign a lot of space in that case).