client: Put indicators in a column layout

A column layout make things easier, we don't have to worry about the
width and children are already laid out properly.
client: Let indicators hide the icon when it's not necessary

Some indicators might contain information without the need for an icon,
when the iconVisible property is false we hide the icon on both the
status area and menu.
client: Date and time indicator

Date and time information is now an indicator, in the future it will
expand into a calendar.