Add a .gitattributes file for line ending settings

It would be nice if the repository contained a .gitattributes file that specifies the line endings since the tslint file requires *.ts files to be LF. 

GitHub's suggestion

text eol=lf 

Git will always convert line endings to LF on checkout. You should use this for files    that must keep LF endings, even on Windows.

I'm not sure if all moodlemobile wants all files to be LF, but here is an example .gitattributes file that would ensure *.ts remain LF:
 

* text=auto 

*.ts text eol=lf