Updates based on current UI

I will attempt to update the images, if I fail, here are the substitutions that should be made:

./media/sendgrid-sign-up/sendgrid_BAR_NEW.PNG -> http://www.screencast.com/t/ORAfB2Y3
./media/sendgrid-sign-up/sendgrid_offerings_store.png -> http://www.screencast.com/t/JQ84OuO0
./media/sendgrid-sign-up/sendgrid_store_scrn2.png -> http://www.screencast.com/t/mpoDjyD8F
./media/sendgrid-sign-up/sendgrid_add-on_dashboard.png -> http://www.screencast.com/t/al1LwcgIor
./media/sendgrid-sign-up/sendgrid_control_panel.png -> http://www.screencast.com/t/awa1ShVT