Fix for #851: Merged from branch 1.5.1:
Added a timer thread, which will try to reconnect to the KNX bus in case
of initial connection failure.
Modified management of DP initialization, such that DPs are not removed
from the queue when connection is not established.
Added debug and trace messages.
Merge pull request #1517 from Snickermicker/pr_851_for_1_6_0

[KNX] Fix for #851: Merged from branch 1.5.1