Add support for refreshing the map data

[gabipetrovay]

It would be nice to be able to post a message to the map to change map properties or marker sources without refreshing the iframe where the map is hosted.

[IonicaBizau]

What's the usecase?

[gabipetrovay]

Imagine a map that you load with no delay of data marker requests. Then, just sending a message to it to load a certain map from a remote source. Now you can have different scenarios:

• Make a directory of maps and switch between without reloading the map or changing pan, zoom, or position.
• Make a map where you display multiple data sources (together in the same time). This means an extra parameter to clear the previous markers or not.

[IonicaBizau]

This is a good idea. There are two related issues:

• Get markers via window messages mono-maps#16
• Show/hide markers via window messages mono-maps#15

We could get the map object and do what we need with it in custom code:

message

Data to be sent to the other window. The data is serialized using the structured clone algorithm. This means you can pass a broad variety of data objects safely to the destination window without having to serialize them yourself. Source: Window.postMessage