Update the old, outdated main stylesheet

- Get rid of Foundation framework
- Include normalize.css as a separate file
- Move general styles from editor.css to the main stylesheet

Apply box-sizing: border-box style to ::before and ::after pseudo elements
Separate input pane and preview pane styles
Shotgun commit:

- Reference panes by position using column.row notation
- Use flexbox to lay out the editor and its components
- Add preferences to allow opening/closing panes without a transition
- Fix bug when opening file while linked to another pane
- Mix in event handling to the Editor class
- Add the wrapMethod preference
- Fix element z-index layering
- Add a number to each pane indicating its column and row, as well as what
  pane it is linked to
- Allow the close command to take the keywords 'all but', which closes all
  panes *except* those specified. Also added the 'this' keyword, which
  will be substituted for the focused pane.
Resize Ace instance after changing input pane mode
Add a default extension for new files, and change the preference key of the default filetype from 'plaintext' to 'default'
Fine-tune link-bar and info-bar element spacing
Move debugging flags above function declarations
Center text vertically on its line in input panes
Fix link line display order issues, and update z-index properties to use multiples of 100.

- This allows the insertion of elements in between existing layers without
  changing other elements' z-index properties.
Implement a vastly improved save command, and add functionality to the FileSystem extension
Tweak animations on link lines
Fix buffer filetypes containing '.' (dot) character
Remove throttling in LinkManager's pane resize listener, but add a note about performance