Final Polish - Remote content browsing UI and ensuring full feature flow is to spec

[marcellamaki]

Observed behavior

While the remote content browsing work is nearly finished, with most issues closed, there should be a "once over" and stitching together of the entire feature flow, and ensuring the front end is to spec, so we can ✅ this issue as complete.

Tasks

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1. Ensure that the Kolibri Library 'pin' is disabled and not clickable
2. Ensure that when there are no pinned devices, some unpinned devices are displayed rather than an empty section and a 'More' button
3. Ensure that when there are no pinned devices, we omit the 'More' header, which is superfluous.
4. Ensure that guest users do not see "partial" information (i.e. headings that are empty or for page sections that they are not able to see; buttons associated with missing/irrelevant sections), etc.