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
Merge branch 'canary' into license-improvements
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
Merge branch 'canary' into license-improvements