Correct typos and reformat code

[maoif]

Corrected some typos,
Changed many tabs to 4-whitespaces,
Reformatted some backend code.

Some changes might be unnecessary. Take them as you see fit.

[mflatt]

Overall, I'm ok with reformatting to remove tabs, but it does complicate tools like git blame, so I would normally leave it alone. Let's see what others think.

There were a few places where tabs has been replaced by 4 spaces but needed 8, so I pushed a small revision here.

[samth]

You can use -w with git blame to ignore whitespace changes. It's also possible to create a repository-level config file that notes particular revisions to ignore for the purposes of git blame.