KIdleTime is a global static, it's destructor it deletes the backend in
a deleteLater; This is *after* the app has been deleted.

This means we end up deleting Poller's ConnectionThread after the static
QVector managing the ConnectionThreads in the main app has been deleted,
leading to a confusing crash.

We can fix this by deleting the connection thread in unload rather than
the actual object destruction.

This fixes a crash on app close, most notably the recursive drkonqi
crash.

Verified what was happening by subclassing the vector and adding debug
Had the drkonqi crash loop, made this change, no more crashes