Implment system request protocol

[BECATRUE]

This PR will close #119.

I implemented the system request protocol as follows.

• When an app emits broadcastRequested signal with channel name swift, _broadcase() in swift handles it as a system call.
• The message is a JSON string with action keys. Possible actions are as follows.
  • "create": Create an app.
  • Its value is a list of dictionaries with two keys; "name" and "info".
  • The value of "name" is a name of app you want to create.
  • The value of "info" is a JSON string of a dictionary that contains the keyword arguments of AppInfo.
  • "destory": Destroy an app.
  • Its value is a list of names of app you want to destroy.

Test

For test, I implemented the test branch, BECATRUE/119/swift-call-test.

In the test, when the generator button in numgen clicked, it emits a system request to destroy logger and create poller.

msg = {
    "destroy": ["logger"],
    "create": [{
        "name": "poller",
        "info": {
            "module": "examples.poller",
            "cls": "PollerApp",
            "show": True,
            "pos": "bottom",
            "channel": ["db"],
            "args": {
                "table": "B"
            }
        }
    }]
}
self.broadcastRequested.emit("swift", json.dumps(msg))

Before clicked

After clicked

[BECATRUE]

For unittest, I think it is efficient to implement tests after developing all features in v2.

[kangz12345]

Hmm.. why the unittest action suffers from segmentation faults?

[BECATRUE]

Hmm.. why the unittest action suffers from segmentation faults?

In my experience, segmentation faults sometime occur in unittest even if it is not fatal problem.

However, in this case, I misimplemented destroyApp() and I think createApp() should be modified. I will fix and update it.

[BECATRUE]

I applied reviews! Please check it.

[BECATRUE]

I updated it.

[BECATRUE]

I applied all reveiws! @kangz12345