Add the possibility to have a custom scope

This line adds the possibility to use a custom scope with $ionicLoading 

I found it useful to show the progress of the loading process.

Demo: http://codepen.io/anon/pen/Ltign
feat(routing): Helpful logging message on unmatched routes
disabled scroll focus for readonly elements
Update ionContent documentation

There are two missing attributes, and one with incorrect details.
Merge pull request #2388 from gnomeontherun/patch-2

docs(ionContent): add missing attributes, remove comment on dead attribute
Merge pull request #2372 from ankri/patch-1

feat(ionicLoading): Add the option to use a custom scope
fix(ionicons): only apply spin to :before, and not the entire element

Closes #2416
fix(ionOptionButton): vertically align content

Closes #2348
fix(scrolling): fix overflow scrolling when side menu and main content both use overflow scrolling. Closes 2201
fix(popup): hide buttons div if there's no buttons to show. Fixes #2344
fix(tap): prevent possible click error in specifc android devices. Fixes #2235
update doc for on function

The on function can take a 4th parameter : options
fix(scroll): calling ionic scroll methods blur any selected input elements. Closes #2244
Merge pull request #2440 from MyBoon/patch-1

docs(): update doc for gesture 'on' function
Merge pull request #2383 from AleksMeshkov/master

fix(keyboard): disabled scroll/focus for readonly elements
fix(pullToRefresh): fix animated icon sometimes not showing
test(pullToRefresh): fix test broken in PR
feat(fonts): platform specific fonts
docs(ion-tab): fix typo in badge css class example

Closes [#214](https://github.com/driftyco/ionic-site/issues/214)
refactor(ionSlideBox): use live nodeList to preserve ordering