Adhoc enhacements try2

These are two patches I made to ad-hoc networks autoconnect behaviour.

The first change, simplifies the autoconnect logic, from a "connect to the first available network you find, or connect to 1 otherwise" to a "connect to the last network you used during this session, or connect to 1 otherwise". This change was made as a requirement from Australia deployment, as the previous behavior seemed too unpredictable for users.

The second change allow us to disable Ad-hoc auto-connect using a gsettings value. Auto-connect option will be enabled by default. When disabled, Sugar will no longer auto-connect until the user explicitly connects to an Ad-hoc network (this is to cover suspend/resume scenarios). When the user explicitly disconnects from the Ad-hoc network, auto-connect will be disabled again.