fix(ADA-1514): Incorrect focus order is observed when Related Files button is activated.

[Tzipi-kaltura]

Description of the Changes

Issue:
when we have more than one attachment/caption the focus move to the last item and not the first

Solution:
shouldFocus is sent as true to downloadItem only if this is the first item in the caption/attachment list and not for all item (and of course also only if this is the first list in the overlay)

improvement of #74

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