Additional search

Added additional search filter options ("lesser than or equal" and "greater than or equal") for int, float, date, time in  src/w2grid.js 

Translation is pending, but I can do it for EN and DE if you merge my changes.

Also added lots of missing semicolons.

Unfortunaltely, my editor is set to delete trailing spaces, so the diff looks worse than it really is.
If you don't care about the spaces and semicolons, it would be enough to merge src/w2grid.js and leave the other 2 files alone.

This is my first time ever working with github, so I hope I've done things right.

---

Off-topic: I'd like to implement a datetime field, and I already successfully tested it as a custom field. 
However it requires to move away from your date and time conversion functions and instead use moment.js  
I would re-write the code, but it would break existing formatting, so please tell me if you see moving to moment.js as an option.

Cheers, Mike