Change Activiti contextroot

[eromano]

Type of issue: (check with "[x]")

- [x] New feature request
- [ ] Bug  
- [ ] Support request

Current behavior:

The context root for activiti api could be changed in the properties instead the JS-API use activiti-app as default not changeable value

Expected behavior:

We should provide a parameter to set the context root value also for the activiti api.

Steps to reproduce the issue:

Node version (for build issues):

New feature request: