client: Merge AppChooserItem into AppChooserDelegate
client: Remove Panel

To implement the status indicator area we must first remove Panel.

Issue: #90
client: Base indicator type

This type defines base properties for all indicators.

Issue: #90
client: Port DateTimeIndicator to the new system

Follow new status indicator changes.

Issue: #90
client: Port UserIndicator to the new system

Follow status indicators changes.

Issue: #90
client: Remove NetworkIndicator and NotificationsIndicator

The former doesn't do much so we postpone it until we have a proper
networking integration and the latter is useless now.

Issue: #90
client: Status area

Add status area with indicators to the Launcher.

Issue: #90
client: Status menu

Aggregate status menu.

Issue: #90
client: Launcher top alignment

Closes #92
client: DateTime service

Closes #93