Refactored names and separated api configs from frontend settings.

Now config in the core_config_dat are under:

• bitbull_instagramwidget/configuration/instagram_token

• bitbull_instagramwidget/configuration/instagram_user_id

• bitbull_instagramwidget/frontend/enabled_homepage

• bitbull_instagramwidget/frontend/instagram_channel

• bitbull_instagramwidget/frontend/number_photos

• bitbull_instagramwidget/frontend/show_like_number

• bitbull_instagramwidget/frontend/frequency

• bitbull_instagramwidget/frontend/cropped_images