Brightcove styling and accessibility fixes

Change description

Fix layout for BrightCove players based on Video.js v7.x+ Styling will break for Video.js 5 but work in ver6 and ver7 and probably forward. Video.js 5 is very old. Small accessibility fix on video player. Fix BrightCove account_id form field appearing blank when instantiating a new XBlock with a default account_id specified in XBlock settings

Type of change

[x] Bug fix (fixes an issue)
[ ] New feature (adds functionality)

Checklists

Development

[x] Lint rules pass locally
[x] Application changes have been tested thoroughly
[x] Automated tests covering modified code pass

Security

[x] Security impact of change has been considered
[x] Code follows company security practices and guidelines

Code review

[x] Pull request has a descriptive title and context useful to a reviewer. Screenshots or screencasts are attached as necessary
[x] "Ready for review" label attached and reviewers assigned
[ ] Changes have been reviewed by at least one other contributor
[ ] Pull request linked to task tracker where applicable

appsembler / xblock-video

Brightcove styling and accessibility fixes #42