[mediacontroller] SendEvent() js tests fixed + code autoformat.

[mediacontroller] SendEvent() js tests fixed + code autoformat.

+ Executed ./code_format script on mediacontroller source code.
+ Fixed invalid tests for MediaControllerClientInfo::sendEvent() method.
+ Fixed minor issues from earlier reviews.
+ initialized all JsonCallbacks to nullptr in constructors of MediaControllerClient/Server

[Verification] tests from test_custom_event.js 100% pass.

Signed-off-by: Michal Michalski <m.michalski2@partner.samsung.com>
Change-Id: I9514897908e8221ed6f1c8eb1c1ed0083bad0996