Major Update To Alpha 0.7.4

This update brings major fixes and code overhauls.

Minor and several major fixes such as:

• Choices now do not require a variable to work in the preview.
• The preview in test game now centers properly.
• The game canvas can now use the scene image aspect ratio.
• Set a min and max size for the canvas.
• Use GIF and Animated WebP files as scene and page backgrounds.
• Changes to the lint & diagnostic code to keep it from missing dead ends occasionally.
• Variables now show up in the test story tab without needing to click the update button (will be renaming the button to just be "Restart".
• Removed unused markdown code.
• Button icon changes.
• More precise movement in the story map flowchart.
• Autosave now uses IndexDB — I overhauled the autosave feature to allow for far more storage for your project. No more out of memory alerts!
• Scene image display controls — Scene images can now be set to use different display modes, such as: cover, stretch, center, and so on... 
• Scene image aspect ratio — You can now set the game/story canvas to use the aspect ratio of the scene image instead of only a 1:1 (square). Control the aspect ratio by using different ratio images. (Overrides the display setting: cover, stretch, center, and so on...)
• Fixed choices in preview — The choices were not working in 0.7.3 unless there was at least one variable added in the project. I fixed it. 

• Game/story canvas Min and Max size — I added a couple of input fields to set the min canvas size and the max canvas size. When using the scene image aspect ratio, these allow the user to use a mix of image sizes and not allow the canvas to grow too big or too small based on the image in a given scene. The overall canvas size can be controlled with these as well, even when not using the scene image aspect ratio.
• And more!