Resolve "Upload snips (images) via e-mail"

Add a new route for image upload

Description:

This pull request introduces a new route for users to upload images/files without the need to open the full labbook on their device. The new route can be accessed via https://labbook_url.de/upload and will show all lab books the user currently has write access to; with the most recently selected on top; and an upload button (file select). Additionally, with mobile browsers, users can directly start the camera with one button.

Feedback and suggestions are welcome.

Changes Made:

• Added a new route
• Direct camera upload
• Same layout as home

Closes #49 (closed)