fix(ngCookie): convert non-string values to string

Previously, non-string values stored in $cookies would be removed, without warning the user, and
causing difficulty debugging. Now, the value is converted to string before being stored, and the
value is not dropped. Serialization may be customized using the toString() method of an object's
prototype.

Closes #6151
Closes #6220
fix(orderBy): support string predicates containing non-ident characters

The orderBy filter now allows string predicates passed to the orderBy filter to make use property
name predicates containing non-ident strings, such as spaces or percent signs, or non-latin
characters.

This behaviour requires the predicate string to be double-quoted.

In markup, this might look like so:

```html
<div ng-repeat="item in items | orderBy:'\"Tip %\"'">
...
</div>
```

Or in JS:

```js
var sorted = $filter('orderBy')(array, ['"Tip %"', '-"Subtotal $"'], false);
```

Closes #6143
Closes #6144
fix(select): avoid checking option element selected properties in render

In Firefox, hovering over an option in an open select menu updates the selected property of option
elements. This means that when a render is triggered by the digest cycle, and the list of options
is being rendered, the selected properties are reset to the values from the model and the option
hovered over changes. This fix changes the code to only use DOM elements' selected properties in a
comparison when a change event has been fired. Otherwise, the internal new and existing option
arrays are used.

Closes #2448
Closes #5994
fix(input): ngMinlength/ngMaxlength should not invalidate non-stringlike values

A regression reported in #5936 shows that prior to cdc4d485a6daa0c74e5d07d8def2a3ee68d93d13, an
input with an ngMinlength or ngMaxlength validator would not invalidate values where value.length
was undefined.

The behaviour of this validator is still incorrect in the case of objects with a length property
which are not arrays or strings, and will most likely remain that way. This cannot change as it is
possibly desirable to use ngMinlength/ngMaxlength in conjunction with ngList.

Closes #5936
Closes #6000