Admin UI for Creating / Modifying / Deleting Indicators

- requires can_edit_data permission at the moment
- domain must be preset in INDICATOR_ENABLED_PROJECTS in localsettings
- a namespace must be specified in INDICATOR_NAMESPACES

example:
```
INDICATOR_ENABLED_PROJECTS = ["mvp-potou", "mvp-sauri"]

INDICATOR_NAMESPACES = {
    'mvp-sauri': (
        ('mvp_indicators', "MVP"),
    ),
    'mvp-potou': (
        ('mvp_indicators', "MVP"),
    ),
}
```