DRY up passing element bounding rects from UIWebView back to Objective-C.

* Centralize string parsing and offsetting in UIWebView method.
* Centralize element bounding rect formatting in util.js (né spoiler.js).
Don't ask to open URL copied from a PM.
Rename "Rendering" group to "Web View Junk".
Document AwfulActionSheet.
DRY up action sheet for long-pressing a URL.
DRY up handling the network activity indicator for UIWebView.

Not 100% sure about this implementation but it's finicky enough that
copy/pasting is not very helpful.
Preserve/restore scroll position in PM view.

* Move the scroll fraction get/set out to a UIWebView property.
Support font scale setting in PM view.
Update thread tags.
Fix disappearing top cell separator in basement.

Things that didn't work:

* Setting the table view's separatorStyle to None and back in
  -tableView:didSelectRowAtIndexPath:.
* Ditto in -tableView:didHighlightRowAtIndexPath: or ...Unhighlight....
* Selecting then deselecting a cell after loading.
* Messing with cells' separatorInset.

Thing that worked but was untenable:

* Setting the table view's allowsSelection to NO. Now the basement is useless.
Formatting.
Formatting and improved Themes.plist usage.
Show Awful Browser modally on iPad.

Messed up the conditional. Meant to say "if we're on iPad **or** there's no
navigation controller to pop onto".
Reset basement separator flag on becoming active
Update Crashlytics.
Allow cancelling beta upload just before it starts.
Also scale username, regdate, postdate, and quotes.

Makes quote size match post size, instead of fixed at smaller.
No longer using system-dynamic sizing.
Switch to SVG clock beside post date.

"Resolution" "independence" "is" "cool" "!"
Replace SVG clock with CSS clock.

SVG creeps me out.

Bonus: try out flexbox for the footer.
Don't split the faux-ellipsis in the post action button when the font scales up.