Add acacia-editor-client dependency

The task `:compileCom_alkacon_opencms_v8_calendar_gwtJava` fails with 18 errors.

An excerpt from the output follows:

````
alkacon-oamp/com.alkacon.opencms.v8.calendar/src/com/alkacon/opencms/v8/calendar/client/widget/CmsSerialDateWidgetFactory.java:30: error: package com.alkacon.acacia.client.widgets does not exist
import com.alkacon.acacia.client.widgets.FormWidgetWrapper;
                                        ^
[...]
alkacon-oamp/com.alkacon.opencms.v8.calendar/src/com/alkacon/opencms/v8/calendar/client/widget/css/I_CmsLayoutBundle.java:40: error: cannot find symbol
    interface I_CmsWidgetCss extends I_Widgets {
                                     ^
  symbol:   class I_Widgets
  location: interface I_CmsLayoutBundle
18 errors
:compileCom_alkacon_opencms_v8_calendar_gwtJava FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':compileCom_alkacon_opencms_v8_calendar_gwtJava'.
````