Adding detailed diff view dialog

Adding an api call for showing a file in prep for side by side view, #126.

Returns pure unparsed text file.  Example of this api call can be seen below.

`/api/show/file?path=/Users/4Tun3C00k13/ungit&sha1=059af219616283aaceaa9efe389bddf8a64b4cca&filePath=source/git.js`