Merging of interpolated class attribute from directive template with replace:true works

Closes #1006

This fixes special characters issue with MongoLab.

https://groups.google.com/d/topic/angular/1T6h7bfZ7Rs/discussion

Changed the isolate scope binding options to:
  - @attr - attribute binding (including interpolation)
  - =model - by-directional model binding
  - &expr - expression execution binding

This change simplifies the terminology as well as
number of choices available to the developer. It
also supports local name aliasing from the parent.

BREAKING CHANGE: isolate scope bindings definition has changed and
the inject option for the directive controller injection was removed.

To migrate the code follow the example below:

Before:

scope: {
  myAttr: 'attribute',
  myBind: 'bind',
  myExpression: 'expression',
  myEval: 'evaluate',
  myAccessor: 'accessor'
}

After:

scope: {
  myAttr: '@',
  myBind: '@',
  myExpression: '&',
  // myEval - usually not useful, but in cases where the expression is assignable, you can use '='
  myAccessor: '=' // in directive's template change myAccessor() to myAccessor
}

The removed `inject` wasn't generaly useful for directives so there should be no code using it.

attr.$observe used to call function only if there was interpolation
on that attribute. We now call the observation function all the time
but we only save the reference to it if interpolation is present.

This is how it worked in rc9, before refactoring $defer into $timeout.

Closes#930