[explore] Split large reducer logic in ExploreViewContainer (#3088)

* split reducer logic for ExploreViewContainer

* fix saveModal component and unit tests

* revert changes in SaveModal_spec.
will make another commit just to improve test coverage for SaveModal component.

* remove comment-out code

* fix merge confilicts

superset/assets/javascripts/explore/actions/saveModalActions.js

@@ -0,0 +1,57 @@
+const $ = window.$ = require('jquery');
+
+export const FETCH_DASHBOARDS_SUCCEEDED = 'FETCH_DASHBOARDS_SUCCEEDED';
+export function fetchDashboardsSucceeded(choices) {
+  return { type: FETCH_DASHBOARDS_SUCCEEDED, choices };
+}
+
+export const FETCH_DASHBOARDS_FAILED = 'FETCH_DASHBOARDS_FAILED';
+export function fetchDashboardsFailed(userId) {
+  return { type: FETCH_DASHBOARDS_FAILED, userId };
+}
+
+export function fetchDashboards(userId) {
+  return function (dispatch) {
+    const url = '/dashboardmodelviewasync/api/read?_flt_0_owners=' + userId;
+    return $.ajax({
+      type: 'GET',
+      url,
+      success: (data) => {
+        const choices = [];
+        for (let i = 0; i < data.pks.length; i++) {
+          choices.push({ value: data.pks[i], label: data.result[i].dashboard_title });
+        }
+        dispatch(fetchDashboardsSucceeded(choices));
+      },
+      error: () => {
+        dispatch(fetchDashboardsFailed(userId));
+      },
+    });
+  };
+}
+
+export const SAVE_SLICE_FAILED = 'SAVE_SLICE_FAILED';
+export function saveSliceFailed() {
+  return { type: SAVE_SLICE_FAILED };
+}
+export const SAVE_SLICE_SUCCESS = 'SAVE_SLICE_SUCCESS';
+export function saveSliceSuccess(data) {
+  return { type: SAVE_SLICE_SUCCESS, data };
+}
+
+export const REMOVE_SAVE_MODAL_ALERT = 'REMOVE_SAVE_MODAL_ALERT';
+export function removeSaveModalAlert() {
+  return { type: REMOVE_SAVE_MODAL_ALERT };
+}
+
+export function saveSlice(url) {
+  return function (dispatch) {
+    return $.get(url, (data, status) => {
+      if (status === 'success') {
+        dispatch(saveSliceSuccess(data));
+      } else {
+        dispatch(saveSliceFailed());
+      }
+    });
+  };
+}