Fixes #699 & $1411
Add version code to themes.js
Change version code of theme.js to 1803
Change version code of theme.js to 1804
Fixes issues for window.onbeforeunload

https://developer.mozilla.org/en-US/docs/WindowEventHandlers.onbeforeunload
> Since 25 May 2011, the HTML5 specification states that calls to
window.showModalDialog(), window.alert(), window.confirm(), and
window.prompt() methods may be ignored during this event.
Merge pull request #1551 from ATofighi/fix-699-1411

Fixes #699 & #1411