Default libraries location should be sites/all/libraries

Modules should not require manual changes to their directory structures after they are downloaded, anything that needs to be installed afterwards, i.e. libraries like modernizr.js, should be kept in a separate location. Following this practice has several advantages - it removes the chance of required files being accidentally removed by the module being updated, it keeps the site's directory structure cleaner by having actual contrib modules in one location and 3rd party dependencies in another location; finally, there's no reason to require libraries be downloaded to the contrib module's directory beyond a bad tradition.

As such, the Modernizr module should not require that the library be downloaded to the module's directory, it should default to loading it from sites/all/libraries/modernizr and it should not require the Libraries module to do this.