Reduce usage of ng-show/hide to reduce number of useless DOM elements (fixed)

Progress in the direction of #87, especially on mobile.
This version doesn't break everything for new users.
Revert "use ng-if to hide date instead of css"

That actually decreases performance, because it adds a watcher to every line

This reverts commit 16365db5889eda5c7c508b3c67ea540338ffae1f.
Merge pull request #270 from glowing-bear/performance3

Performance improvements (fixed)