🐛 Fix image url fetching, setting default user_agent

[jjtbsomhorst]

What have I done:

• bumped various packages
• Introduced a new method user_agent that lets you set the user agent being used in the class
• When the user agent is not the default user agent it will use this user agent for fetching images. This solves an issue I had that in some circumstances the image host returns 403 when retrieving the headers without using a proper user agent.
• Made some minor tweaks