finatra/doc: companion material links are broken on the presentations page

Problem:

The current links to companion material do not resolve

Solution:

Find and substitute working companion material links

JIRA Issues: CSL-10721

Differential Revision: https://phabricator.twitter.biz/D779310

Author: DinoCassowary

doc/src/sphinx/presentations/index.rst

@@ -6,14 +6,14 @@ Finatra Presentations
 October 2015
 ------------
 
-- Twitter #Flight Developer's Conference - `Finatra: The Fast, Testable, Scala Framework Powering Twitter APIs <https://g.twimg.com/dev/flight/2015/keynotes/Flight2015-Cosenza_Steve-Finatra.pdf>`__ 	· `Youtube Video <https://youtu.be/IFCbSIvdka8>`__
+- Twitter #Flight Developer's Conference - `Finatra: The Fast, Testable, Scala Framework Powering Twitter APIs <https://youtu.be/IFCbSIvdka8>`__ (YouTube Video)
 
 August 2015
 -----------
 
-- `#FinagleCon 2015 <https://finagle.github.io/finaglecon/>`__ - `Streaming HTTP with Finatra and AsyncStream <https://schd.ws/hosted_files/finaglecon2015/d1/Streaming%20HTTP%20with%20Finatra%20and%20AsyncStream.pdf>`__ 	· `Youtube Video <https://youtu.be/7dsX0S0WsEk>`__
+- `#FinagleCon 2015 <https://finagle.github.io/finaglecon/>`__ - `Streaming HTTP with Finatra and AsyncStream <https://static.sched.com/hosted_files/finaglecon2015/d1/Streaming%20HTTP%20with%20Finatra%20and%20AsyncStream.pdf>`__ 	· `YouTube Video <https://youtu.be/7dsX0S0WsEk>`__
 
 April 2015
 ----------
 
-- `SF Scala <https://www.meetup.com/SF-Scala/>`__ at Twitter - `Introducing to Finatra 2.0 </finatra/Presentations/FinatraSFScala.pdf>`__ 	· `Youtube Video <https://youtu.be/hkVp9W4c9bs>`__
+- `SF Scala <https://www.meetup.com/SF-Scala/>`__ at Twitter - `Introducing to Finatra 2.0 <https://blog.twitter.com/engineering/en_us/a/2015/finatra-20-the-fast-testable-scala-services-framework-that-powers-twitter>`__ 	· `YouTube Video <https://youtu.be/hkVp9W4c9bs>`__