[Feature] Add ExperimentalFeatures feature with dummy example

[arielj]

This PR adds a new concept of Experimental Features that we can use when developing new stuff that we add into heroic (new design, new stores, some shiny new feature, whatever).

It shows a list of features in the Advanced settings and users can opt-in to help test new features before they are marked as stable.

It's added with a dummy sample on how to use it and how to add flags to configure:

experimental.mp4

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Use the following Checklist if you have changed something on the Backend or Frontend:

• Tested the feature and it's working on a current and clean install.
• Tested the main App features and they are still working on a current and clean install. (Login, Install, Play, Uninstall, Move games, etc.)
• Created / Updated Tests (If necessary)
• Created / Updated documentation (If necessary)

[flavioislima]

Looks good, but are we keeping the shiny feature? only if you make Heroic shine :P

[arielj]

Looks good, but are we keeping the shiny feature? only if you make Heroic shine :P

hahaah, it could be an easter egg to add some shiny effects xD