Added support for new Reddit. Collapsing a large comment thread will now keep the collapsed comment on screen instead of leaving you much further down the page. Otherwise leaves the native collapsers untouched.

Old Reddit works as before.

Adds extension preferences for:
* Switching themes - choose between the new "Minimalist" theme or switch back to the old "Retro" theme.
* Disabling the scroll-to animation when collapsing a thread that starts off-screen.

+ Reddit Comment Collapser has been completely reworked to be much more lightweight and faster
+ A new more subtle theme and collapser with greater consistency across subreddits.