redirect "Reference Apps" ecosystem pages to MDN pages (bug 1022029)

https://bugzilla.mozilla.org/show_bug.cgi?id=1022029

Old pages:

https://marketplace.firefox.com/developers/docs/apps/chrono
https://marketplace.firefox.com/developers/docs/apps/face_value
https://marketplace.firefox.com/developers/docs/apps/podcasts
https://marketplace.firefox.com/developers/docs/apps/roller
https://marketplace.firefox.com/developers/docs/apps/webfighter
https://marketplace.firefox.com/developers/docs/apps/generalnotes
https://marketplace.firefox.com/developers/docs/apps/rtcamera

In addition to adding all the proper redirects, I've also cleaned a few grammatical errors and inconsistencies across the MDN pages:

https://developer.mozilla.org/en-US/Apps/Reference_apps
https://developer.mozilla.org/en-US/docs/Web/Apps/Reference_apps/Chrono
https://developer.mozilla.org/en-US/docs/Web/Apps/Reference_apps/Face_Value
https://developer.mozilla.org/en-US/docs/Web/Apps/Reference_apps/Podcasts
https://developer.mozilla.org/en-US/docs/Web/Apps/Reference_apps/Roller
https://developer.mozilla.org/en-US/docs/Web/Apps/Reference_apps/Webfighter
https://developer.mozilla.org/en-US/docs/Web/Apps/Reference_apps/General_Notes
https://developer.mozilla.org/en-US/docs/Web/Apps/Reference_apps/rtcamera

r? @ednapiranha @clouserw @diox