refactor(filters): move responsibility for adding empty data item int…

…o select.html template

Adding an empty option to the array returned by `$column.filterData` only makes sense when
using that array as the datasource for the `select.hmtl` template.

Therefore the responsibility for doing this should be moved into this template.

This allows the `$column.filterData`  to provide a suitable datasource for custom templates that
might not want an empty option.

This commit also fixes a problem where `$column.filterData` is used in more than one ngTable.
In this scenario duplicate empty items would be added to the array.

BREAKING CHANGE:

`ngTableController` no longer adds an empty item to the array returned by `$column.filterData`.

This will only affect those apps that were using `$column.filterData` to supply data to a *custom*
filter template.

Those apps that are using the `select.html` will be unaffected as the `select.html` filter will add
this empty item.

src/ng-table/filters/select.html

@@ -1,4 +1,5 @@
-<select ng-options="data.id as data.title for data in $column.data"
+<select ng-options="data.id as data.title for data in $selectData"
+ ng-table-select-filter-ds="$column"
  ng-disabled="$filterRow.disabled"
  ng-model="params.filter()[name]"
  class="filter filter-select form-control" name="{{name}}">

src/scripts/ngTableController.js

@@ -128,28 +128,15 @@
  if (!angular.isArray(data) && !angular.isFunction(data) && !angular.isObject(data)) {
  // if none of the above was found - we just want an empty array
  data = [];
- } else if (angular.isArray(data)) {
- ensureEmptyListOption(data);
  }
  $column.data = data;
  });
  }
  // otherwise, we just return what the user gave us. It could be a function, array, object, whatever
  else {
- ensureEmptyListOption(result);
  return $column.data = result;
  }
  });
-
- function ensureEmptyListOption(data){
- if (!angular.isArray(data)){
- return;
- }
- data.unshift({
- title: '',
- id: ''
- });
- }
  };
 
  this.buildColumns = function (columns) {