fix(FEC-12350): external captions shown while cc button disabled

[lianbenjamin]

the issue:
when captions are external and disabling cc button, captions are still shown on player.

root cause:
player's API hideTextTrack() does not handle external captions.

Description of the Changes

• check if active text track is external and use hideTextTrack() API of externalCaptionsHandler

Solves FEC-12350

CheckLists

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• test are passing in local environment
• Travis tests are passing (or test results are not worse than on master branch :))
• Docs have been updated