Add gamepad light indicator extension

[fernando-80]

Closes #67

The following tasks have been completed:

• [ ] Modified Web platform tests (link to pull request)

Implementation commitment:

• [ ] WebKit (https://bugs.webkit.org/show_bug.cgi?id=)
• [ ] Chromium (https://bugs.chromium.org/p/chromium/issues/detail?id=)
• [ ] Gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=1523351)

[fernando-80]

@nondebug @knyg @sagoston light-indicator extension PR ^^^

[marcoscaceres]

Hi @fernando-80, could you kindly please join the WebApps working group? That will make the IPR bot happy.