Refactor filters

The filters are being simplified to something similar to Excel autofilter.

Each column has a new property now `filterable: true # or false`. If set to true - a filter form field will be rendered for that column.

The filters builder section has become obsolete. The `filterType` option is used in FilterType, the `formType` option is used in NewType and EditType. The `formOptions` are used in both cases. If you need a completely diffrent set of options for the filterType - you need to customize the FilterType.