[cutes] extension libraries are handled by separate entity

And QLibrary is shared between different environments and unloaded
only if not used by any.

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[cutes] cutes.gc() method

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

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[tests] correct paths for qml import etc.

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[actor] more reliable actor hold locks management

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