Move from connect() to connectObject() where applicable

[stuarthayhurst]

connectObject() allows tying the lifetime of the connection to the lifetime of another object. If the connected object or the object its lifetime is tied to is destroyed, the connection is destroyed (uses the destroy signal).

This means in several cases we can just use connectObject() to tie the lifetime to this, and we don't need to track any signal IDs, as its destruction will be taken care of for us. Another benefit is that we can connect multiple signals in 1 call, by repeating 'signal', handler each time as arguments, instead of duplicating the call.

Any unused signals were also removed :)

[stuarthayhurst]

317 includes this, as it was branched from this branch

Closing in favour of that instead