Scope scrict mode to IIFE

[gcziprusz]

Using a file level 'use strict' has the potential to force other libraries into ES5 strict mode and cause issues when minified.

The underlying CodeMirror library will break for example.

this becomes undefined instead of the expected window object:
https://github.com/codemirror/CodeMirror/blob/4bdf6440429bc455f4ce39486d424fba0be7fa14/lib/codemirror.js#L16

[gcziprusz]

@douglasduteil this strict issue fix should take care of a couple other outstanding PR's like #50 and #39

[magmel48]

+1