amd support added

Hello, Tony

This PR adds support of loading jqGrid with requirejs
i think if you are going to make jqGrid a commercial product
(as you mentioned here http://www.trirand.com/blog/?p=1173)
this is very useful option

- i was tried to change only places required for amd support i mean i was trying to make no additional code formatting but git doesn't think so. sorry(
- grid.tbltogrid.js is not looks like part of code so i did nothing to it, will fix it if you tell me how to test
- grid.locale-bg1251.js and grid.locale-hr1250.js looks broken, so maybe i need some help with them
- also i moved plugins inside js dir, for better paths', don't know if you like this, but keeping them on same level with code was made it difficult to use them as dependencies
- there are also ton of example of how to use jqGrid with and without bower and requrejs, so no old code will be broken by this commit
- some examples are also regression tests, i can add more but i don't know more real cases
- there is also Gruntfile.js configured for making a build of entire jqGrid with all plugins