[WIP] Feature multi apps

[edgurgel]

It closes #27

This PR will make Poxa accept a new parameter as part of the configuration:

apps: [{"app_id2", "app_key2", "secret2"}]

The apps parameter will need to map nicely to something that conform understands so poxa.conf will be simple to maintain. The above configuration may change.

The old way will also be accepted and merged with this new parameter.

Missing:

• Change app configuration check from poxa.ex so it outputs how many apps are configured.
• More integration tests to test isolation between apps;
• Update poxa.conf to support multiple apps;
• Update README with the new way to configure multiple apps.

[arrowcircle]

@edgurgel How its going with multiapps? I have thoughts about configuration.
First of all, if key and secret set via env, it should run in single app mode ignoring config.
Multiapp is only usable via config file. What do you think?

[edgurgel]

I would like to use just the config file through conform, but I can't find a nice way to handle a list of configured apps through conform's DSL :/

[Alir3z4]

Wish this could get any progress.