Feature/use strict compliance

Some of the variable declarations didn't use the `var` keyword. This adds them to the window object as globals, which probably isn't intended. This isn't a big deal generally, but it causes the library to fail when it's included in a page where `"use strict;"` is set in the global scope. 

Which admittedly is not a great idea, but I had to deal with it recently on a project and I made these changes to the library, so I figured I might as well share upstream.

On a side note, when I ran `grunt` the LESS generated slightly different CSS (more specific selectors, e.g. `tr > span.foo` to `tr > td > span.foo`), and the linter threw a couple of errors. I didn't include it in these commits, but it might be something to look into.

```
Running "csslint:strict" (csslint) task
Linting css/footable.core.css...ERROR
[L9:C3]
>> Expected RBRACE at line 9, col 3. This rule looks for recoverable syntax errors. (errors)
[L15:C1]
>> Unexpected token '}' at line 15, col 1. This rule looks for recoverable syntax errors. (errors)
Linting css/footable.core.min.css...ERROR
[L1:C356]
>> Expected RBRACE at line 1, col 356. This rule looks for recoverable syntax errors. (errors)
[L1:C480]
>> Unexpected token '}' at line 1, col 480. This rule looks for recoverable syntax errors. (errors)
Warning: Task "csslint:strict" failed. Use --force to continue.
```