Spatial query form fixes

* Export button fixes.
 * Review retrocompatibility for show CSV
 * Allow file export for complex filters
 * New option `exportDoubleCheck`: Flag to make check before export
 * Fixes IE 8 bug on feature grid plugin (on export action)
 * Fix feature grid layout for IE
 * Select `CSV` as default export for the export window.
* Refactor spatial selectors methods
 * Refactor code of the spatial selector methods as widgets instead plugins to fix #339 issue.
 * Optionally add a geometry operation combo for the spatial filter

This commit is related to those issues:

* fixes #335
* fixes #339
* fixes #345
* fixes #346

Also, I've done some changes on wiki pages in order to harmonize with this code:

* [Gecoder plugin](https://github.com/geosolutions-it/MapStore/wiki/Custom-Geocoder-based-on-WFS)
* [Spatial selector query form plugin](https://github.com/geosolutions-it/MapStore/wiki/SpatialSelectorQueryForm-Plugin)
* [Feature Grid plugin](https://github.com/geosolutions-it/MapStore/wiki/Feature-Grid-Plugin)
Remove old code from geocoder

Remove bad lines from the older version of the spatial selectors (when those are plugins)
Translations fixes

Rename spatial selector methods in translation files.
Merge pull request #354 from alediator/spatial_query_form_fixes

Spatial query form fixes