Added ng-animate angularjs module to add animations to the app.
Removed bootstrap panel classes from entries list. Opening and closing entries is done with a ng-show directive, instead of adding and removing the "in" class (which is associated to bootstrap collapsible panels).

The reason is that we use very little of the bootstrap panels features. It's more convenient to use the ng-show directive to open/close entries instead of ng-class; this way we have support for animations from angularjs with minimal work.

The entries list looks a bit different (thinner borders, square instead of rounded corners in each entry) but actually I think it looks better now.
Removed bootstrap panel classes from the sidebar. Open/close folder in the sidebar with ng-show, instead of adding/removing the "in" class.

We were using very little of the feature set of bootstrap's panels. We will roll our own solution. Also using ng-show instead of ng-class gives us support for animations using angularjs with minimal work.
Removed rounded corners in sidebar folders.

It looks more metro-like with sharp corners.
Fix tests.
Fix tests.
Fix tests.
Fix tests.
Fix tests.
Simplified sidebar folder markup by removing an unnecessary div.
Use CSS transitions to animate opening/closing folders.

It's a bit complex because besides transitions in the folder content, transitions in the margins and padding of several sub-elements have to be added as well (otherwise the margins-paddings of those elements disappear suddently at the end of the animation, which causes a jerky effect).
Rotate the sidebar folder arrows 90 degrees clockwise when opening a folder, and 90 degrees counter-clockwise when closing it.
Minor changes in SCSS format and comments for better readability.
Minor change in styles.
The styling of open/closed folders in the sidebar is performed with ng-class instead of ng-show.

When the folder is open, an "open-folder" CSS class is added; otherwise a "closed-folder" class is added. While angularjs is deciding which class to apply, the folder contents are hidden (display: none).

The reason is that this makes animations simpler. Using ng-show or ng-hide made animations more complex, because in firefox the sudden change from display: none to display: block sometimes made the folder contents appear suddenly, instead of a smooth animation. Chrome did not exhibit this behavior.

I've decided to use separate classes to indicate if a folder is open or closed, and to animate the transitions between them.

Also the small move upwards of the folder arrow when it's opened (to compensate the fact that the icon has bigger width than height) is also animated with a transition instead of sudden. It's just 1px so it's probably not noticeable.
Fixed tests.
Removed unnecessary CSS transitions.

The animation looks good enough without them, and removing them improves performance.
Removed unnecessary ng-cloak class.
Removed redundant nested div in entries.
Added back missing padding in entry-panel.