SOL-20 add content type filters instead of extension, fix css issues, ad...

[dino-cikatic]

...d filter text to pagination header

@martynjames this is a branch implementing SOL-20 fixes. It is pushed to solutions because I don't have permissions to push it to platform.

[openedx-webhooks]

Thanks for the pull request, @dino-cikatic! I've created OSPR-246 to keep track of it in JIRA. JIRA is a place for product owners to prioritize feature reviews by the engineering development teams.

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[chrisndodge]

Hi @dino-cikatic there are a few pep8 violations and a few failing JS unit tests (you can see them listed in the build report). Thx.

[martynjames]

Closing to keep feature work within solutions fork until ready to submit to master