Merge pull request #1 from deztructor/master

Fixes in memory management and usage of isolates
[doc] CUTES_TRACE is documented

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[cutes] cutes.setEnv(name, value)

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
no warning if on_reply/progress is not callable

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[actor] trace error passing

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[actor] pass only valid error fields

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