Refactored multi-file data structure

What does this MR do?

This moves away from storing in a single array just to render the table. It now stores in a multi-dimensional array/object type where each entry in the array can have its own tree. This makes storing the data for future feature a little easier as there is only one way to store the data.

Previously to insert a directory the code had to insert the directory & then the file at the right point in the array. Now the directory can be inserted anywhere & then a file can be quickly added into this directory.

The rendering is still done with a single array, but this is handled through underscore. Underscore takes the array & then goes through each item to flatten it into one. It is done this way to save changing the markup away from table, keeping it as a table keeps it semantically correct.