Switching GATT connection to newly provisioned node

[philips77]

In some situations it is useful to connect to a newly provisioned node using GATT Proxy instead of relying on transporting messages over ADV Bearer. This is especially true for Low Power Nodes (LPN), which need to establish friendship before they can exchange messages. However, they may be open for GATT connections.

This PR adds a feature allowing to switch the GATT connection to a newly provisioned node. When the phone was connected to another GATT Proxy at the time of provisioning, a new dialog will be displayed allowing to disconnect it and connect to the new node.

Note
This will only work if the node doesn't change MAC address when switching to Mesh Proxy service.

[philips77]

This PR also fixes #498. The NetworkConnecion class has several issues:

• disconnectCurrent() was disconnecting only the first proxy. It might be, that the first one was not connected
• scanning was started when Automatic Connection was being enabled, even if the connection was already established