Need to show appropriate error message in cases of UI failures

Need to show appropriate error message in cases of UI failures.

Scenario 1 : When user tries to import invalid workflow xml. For example, if user imports coordinator xml instead of workflow, then appropriate error message should be displayed. Same should be handled for bundles and coordinators.

Scenario 2 : When user tries to import larger workflows. Currently workflow manager supports workflows with 400 nodes. If user imports workflows with more nodes, then appropriate error message should be shown.