A new UI once more

[davidpkj]

Hi all, so this is yet another attempt to get a new UI for this project. This PR is largely based on doebi's work at #265 with some additions like:

• Fixed issues like
  • Multiple HTML5 Backends
  • Upload failing with uppercase extensions
• An updated home page with useful tips
• Unified most style rules to SCSS files
• Unified main UI logic under JSX files
• A beautiful brown color scheme

Let me know what you think! (I heard three time's the charm 😉)

[ddvk]

Hey, thanks a lot for putting the effort in, it looks very nice.

there are a couple of minor issues:

• uploading a file doesn't refresh the tree (I know the current implementation is also hacky and I never got to implementing live updates)

• the UI doesn't use the whole browser window on a large display (my main gripe)
  
  vs
  

• when a document has been selected, there is no way to upload another document (should first select folder)

[davidpkj]

Hey, glad you like it! I have now fixed the first two issues, but would like to leave the third behavior as is. My reasoning being:

• It is clearer/more explicit which folder the file will be uploaded to
• It's not difficult from a UX perspective to select a folder beforehand (to either use the path above the file preview or the file tree to the left)
• The upload box would get in the way on mobile devices with small screens. This leaves more space for the preview while having to scroll less.

Let me know what you think.