Provided dependencies

[SmasSive]

Change glide and picasso to provided dependencies. Solves #3

[SmasSive]

@CristianGM I've done this change but I don't really like too much the new configuration, I think it makes more difficult to use the project.

In order to simplify as much as possible the configuration, I was thinking about a new module that simply adds the required dependency, this way user don't have to know anything about which dependencies she has to add.

An example would be:

compile 'com.schibsted.spain:prado:1.0.0'
compile 'com.schibsted.spain:prado-picasso:1.0.0'

The second dependency will add picasso and picasso2-okhttp3-downloader dependency.

What do you think?