Added indentation linting

This adds an indentation linter.

- Checks that all indentation white space is the configured char
- Checks that the number of indentation chars is dividable by the configured indentation number

Example of custom configuration:
``` javascript
{
    "tool": "indentation",
    "include": ["**/*.js", "!node_modules"],
    "config": {
        "indentChar": " ", // Defaults to "\t"
        "indentNumber": 4 // Defaults to 1
    }
}
```