Update README.md
docs(*): ensure all dist files contain a license header
Changed Gruntfile:
- extended concat task with banner configuration for each lib_file
- Added exclamation mark to the banner to prevent deletion of banner
  during uglify
- added preserveComments option to uglify task to preserve license
  header.
- registered the concat:banner taskts for each lib file.

Partially resolves #428
chore(*): cleanup obsolete grunt config

Since src/service/default-interpolation.js moved from lib_files.ext to
lib_files.core some time ago, some grunt configuration became obsolete.

- Removed obsolete default_interpolation configuration
- Removed obsolete build:default_interpolation grunt task
chore(Gruntfile): ensure all dist files contain a license header
Changed bower.json:
- added licenses array so that the MIT licence is added to the license headers

Partially resolves #428
fix(package.json): fix repository url
fix(demo): correct demo of `translate-values`
feat(service): add possibility to translate a set of translation ids

This enriches both `$translate()` and `$translate.instant()` with the
possibility to call them with an array rather than a string. This makes
the API more comfortable in some situations.

```javascript
// for example...
$translate(['FOO', 'BAR']).then(function(translations){
  console.log(translations.FOO);
  console.log(translations.BAR);
});
// ... and
console.log($translate.instant(['FOO', 'BAR']).FOO);
console.log($translate.instant(['FOO', 'BAR']).BAR);
```
feat(directive): add option to define a default translation text

This adds an optional opt-in feature:

```html
<span translate=„my.key.for.a.welcome.message“ translate-default=„Welcome {{username}}!“></span>
```

or even

```html
<span translate translate-default=„Welcome {{username}}!“>my.key.for.a.welcome.message</span>
```
Update autogenerated documentation on how $translate is used
fix($translateProvider): fix comparison in one case of negotiateLocale()
tests($translateProvider): add test for locale negotiation w/o aliases
fix(service): docs annotation
docs(guide/uk,ru): Translate Migration Guide to Russian and Ukrainian

Translate the Migration Guide chapter of the  Guide to Ukrainian and Russian languages.
docs(guide/en): fix typo
feat(directive): Support for camel casing interpolation variables.

When using a directive with interpolation variables with camel cased
words (camelCase), there was no nice way to specify the values of the
variables with the `translate-value-*` attributes.

You can specify attributes like this `translate-value-first-name="Glenn"`,
which would work together with this translation string `'Hello {{firstName}}'`.
fix($translate): use case-insensitive check for language key aliases

When language key aliases are available they are now compared to the browsers locale in a case-insensitive manner.

Closes Issue #431
Fixes for a few typos.
fix($translate): if translation exists, use the translated string even if it's empty
Adding Simplified and Traditional Chinese documentation, update the links and enable language chooser for those 2 lanugages.
fix(directive): Make translate-value-* work inside ng-if and ng-repeat

Closes Issue #433