bower.json overrides declaration

The injector task can now exploit the use of bower override
declarations for instances where libraries do not explicitly declare
the keyword  and value for “main” in order to determine the correct
location of distribution artefacts.

To support this the injector task method: getFilesFromBower has been
refactored to utilise the latest stable wiredep version 1.7.0. The
latest version has an official programmatic access route, thus no
longer requiring the need to tap into internal module exports.