flickr plugin ignores command line configuration

[sandipb]

Currently the flickr plugin tries to initialize flickraw at the time of import. Since there is no other way to access the site configuration which ois already loaded, a default command line parameter override is used to generate a new site config from which the flickr configurations is picked up.

The problem is that if I use jekyll command line parameters like "--config _config.yml,_config_extra.yml", the flickr configuration is not picked up if it is mentioned in the second file.

In this patch, I am moving the initialization from import-time to render time where the context provides all the final configuration. (Reference issue)

I am new to ruby, so I would completely understand if you do not find my code ruby-ish and prefer a cleaner alternative. I just wanted to keep my copy of the plugin in sync with your repo. :)

[neilk]

I'm reviewing some stuff I didn't get around to in 2015. I'm sorry this PR has sat around for so long without any communication. I'll try to find time to deal with it over the holidays.