Clean out the .gitignore

Some exclusion in the root ```.gitignore``` could be elsewhere to keep the core upgrade easy.

I think only one line is necessary besides the original lines.
``` files/* ```

The best way to exclude the IDE/TextEditor files is add the following lines to ```~/.gitconfig```.

```ini
[core]
	excludesfile = ~/.gitignore
```
And create file like this: https://gist.github.com/Sweetchuck/6143692