add 'nu' and 'nn' in $.jgrid.search.odata for en, de, ru, fix formatting

Hello Tony,

the current version of jqGrid doesn't display `"nu"` ("is null") and `"nn"` ("is not null") operations even if one explicitly specify there in the array `searchoptions.sopt`. The reason is missing entries in `$.jgrid.search.odata` of all `grid.locale-XX.js` files. The method `searchGrid` calls `jqFilter` with the option `ops : p.odata` (see [here](https://github.com/tonytomov/jqGrid/blob/v4.5.4/js/grid.formedit.js#L163)). Later (see [the lines](https://github.com/tonytomov/jqGrid/blob/v4.5.4/js/grid.filter.js#L371-L375)) `jqFilter` uses elements of `sopt` array only which can be found in `ops` (so which can be found in `$.jgrid.search.odata`). jqGrid 4.4.5 used `ops` directly in `grid.filter.js` and the `ops` had entries for `"nu"` and `"nn"` (see [here](https://github.com/tonytomov/jqGrid/blob/v4.4.5/js/grid.filter.js#L71-L72)). Some later modification of jqGrid code follows removing of `"nu"` and `"nn"` entries.

I added  `"nu"` and `"nn"` in `$.jgrid.search.odata` only for en, de, ru languages. The same changes are required for all other language files. Additionally I fixed in `grid.locale-de.js` and `grid.locale-de.js` formatting by replacing multiple spaces by tabs like it will be already used in the rest of the code.

Best regards
Oleg