[Admin] Bug fixes for Activity Themes and add validation checks for pricing rules

[yow-yiying]

• [x] 1. Bug: When editing a theme, not able to save unless theme name is edited
• [x] 2. Bug: When client shops for activities, disabled themes should not be shown to clients
  
• [x] 3. Bug: When vendors create activities, disabled themes should not be allowed for selection
• [x] 4. Prof feedback for SR1: When vendor/admin set pricing rules for an activity, add some validation checking to make sure that when number of pax increases, price per pax should either go up or go down (shouldn't be random) Eg: When "Next" is selected, warning message should display