Filter containers to notify

[tarasov65536]

This PR gives ability to specify set of filters to containers query when new generated file arrived.

It is kinda similar to #311 but with better implementation from architectural point of view.

It introduces new command line argument -notify-filter that adds filter in list of filters to query containers that should be notified when generated file changed. Argument format as in docker api

For example:

docker-gen -notify-filter name=foo -notify-filter label=bar=baz ...

adds two filters to containers query.

Signal code still defined by argument -notify-signal.

[josegonzalez]

This probably needs a test in order to get merged.

[tarasov65536]

@josegonzalez, what kind of test it needs? Can't find anything similar.