gs-details-page: Collapse long descriptions

Add a button to Read More/Read Less of the application description, starting
with the collapsed state.

Closes #11
Closes !514
2 jobs for 11-collapse-long-descriptions in 5 minutes and 3 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #908368
debian-stable-x86_64

00:02:57

passed #908367
fedora-x86_64

00:05:03