fix(modal): respect autofocus on child elements

Auto-focusing of a freshly-opened modal element causes any child
elements with the autofocus attribute to loose focus. This is an issue
on touch based devices which will show and then hide the onscreen
keyboard. Attempts to refocus the autofocus element via JavaScript will
not reopen the onscreen keyboard. Fixed by updated the focusing logic to
only autofocus the modal element if the modal does not contain an
autofocus element.

Fixes #1696
Closes #1892
Closes #2273
fix(dropdown): remove `C` restrictions to avoid conflicts

Fixes #2156

BREAKING CHANGES: Both `dropdown` and `dropdown-toggle` are only attribute directives

Before:
  ```html
  <btutton class="dropdown-toggle" ...>
  ```
  After:
  ```html
  <btutton class="dropdown-toggle" dropdown-toggle ...>
  ```

Closes #2170
docs(CONTRIBUTING.md): clarify GitHub issues handling policy
docs(contributing): fix typos

Closes #2566
fix(typeahead): replace ng-if with ng-show in matches popup

Fixes #2474
Fixes #2541
Fixes #2293
Closes #2535
Closes #2557
fix(modal): controllerAs not checked

This causes the controller to be added to the scope as a property "undefined"!

Closes #2564
docs(README): use svg instead of png to get better image quality

Closes #2629
fix(datepicker): memory leak fix for datepicker

Fixes #2658
Closes #2684
fix(datepicker): Fix date picker performance problem.
Each datepicker creates around 300 watches.
Having a few datepickers on a page will cause
serious performance problems.
Merge branch 'master' of https://github.com/corystevens/bootstrap