Merge pull request #2 from deztructor/master

[subscriber] changed() is emited on subscription
more error logging

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[subscriber] shared pointer for property monitor

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[tools] contextkit-monitor

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
consistent onX() name for changed slot

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
compromise between reopen speed and power saving

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[subscriber] subscribed only if opened

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[subscriber] target was not removed on unsubscription

it was erased from the copy of targets set successfully and it resulted
in that target was not connected to the source on resubscription and
updated on value changes

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[subscriber] always notify on unsubscription

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
error logging

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
internal subscribe_() executes despite the state

only called from client it returns cache_ if it is subscribed already

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[subscriber] reverting to use value cache again

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
cosmetic changes

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
do not emit excessive signal

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[subscriber] event can be skipped if notifier is disabled

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
Merge pull request #3 from deztructor/reliability

Fixes for issues with unsubscription and skipping of poll notifications