Strengthened warnings to remember passphrase

@stroilova, @srpearce, please take a look. Fixes DOC-860.
Merge pull request #5102 from edx/ahodges/doc/DOC860

Strengthened warnings to remember passphrase. Fixes DOC-860.
Video link obfuscation. [BLD-1230]
Added some Jasmine unit tests.
Add improvements.
Add a11y.
Few fixes.
More fixes.
Fix positioning.
Test correct a11y.
Add fix.
Fixed 'always block in Jasmine tests.