New file format

[Philip-Scott]

While using JSONs as a file format is good, it has a lot of limitations such as always having to open completely the file in order to view it's contents, as well as images being almost 30% larger due to having to make them into base64. Being able to store files as a Zipped file brings support to a lot of things, most importantly being able to include a "git repo" inside every presentation to store multiple versions of said files.

Proposed Folder Structure:

• content.json The json with the slideshow data
• styles.json Json with text styles, and other type of data
• version File which holds the current version of the file. For future proofing
• index.html The HTML file with the JS to keep html rendering support
• thumbnail Just a link to the thumbnail file at /Thumbnails
• /Pictures/ For images.
• /Thumbnails/ To store the slide thumbnails
• /Videos To store videos (Future feature)
• /Shapes To store SVG shapes (Future future)
• /.git/ The place for the git repo. (Future feature)

Pictures, Thumnails and others are stored with randomized file names to prevent collisions, and could be re-used in multiple places while only storing one file

TODO:

• Move images from content file to /Pictures
• Move thumbnails from content file to /Thumbnails
• Fetch file thumbnail from content file, and store it as cache
  • To prevent reading from multiple mb of files just to render the initial images
• Make a SpiceUpFile the central place to manage all files and images
  • This should handle object creation and deletion when slides and canvas items are hidden
• Re-add Image tests
• Update debian control file for new libarchive dependency
• Duplicated images will now use the same file. Can be "Unlinked" though the image toolbar

Fixes #220