Allow via web form update all config app options. Closes #319

This commit allows users to modify via a web form the next two new items:

 * Scheduler (you can choose from all the available ones)
 * Image Icon URL for your app
Fix the test_admin create and update app methods. Refs #319
Merge pull request #324 from PyBossa/issue-319-edit-all-app-info

Allow via web form update all config app options. Closes #319