Handling of shunting times (de: Verwendung von Rangier-/Verschub-Zeiten)

Description

There are two different ways to define shunting time in the current railML version 2.4.

Suggested change:

• at least one @shuntingTimes should become deprecated from a future railML version

### Background
Besides the existing attributes such as `@commercial`, `@stopOnRequest`, `@onOff`, etc. it shall be possible to provide the reason/purpose of stop not just as a free-text field that is currently availble using the attribute `@purpose`.

Links

• Forum discussion
• Dirk Bräuer (iRFP) (en), June 2018: Meaning and usage of @shuntingTime
• Wiki Documentation
• TT:stopTimes
• TT:ocpTT

## Changes in railML 2.X
All activities taking place during a stop can be documented using the new enumeration values for the type of activity taking place at a stop. 

### railML elements
The following new elements are available:
 1. ` railml/timetable/trainParts/trainPart/ocpsTT/ocpTT/stopDescription/stopActivities `
 1. ` railml/timetable/trainParts/trainPart/ocpsTT/ocpTT/stopDescription/stopActivities/stopActivity `
 1. ` railml/timetable/trainParts/trainPart/ocpsTT/ocpTT/stopDescription/stopActivities/stopActivity/@type `
The following XSD file(s) have been updated:
 1. timetable.xsd
 1. timetableTypes.xsd

### Changesets in trunk
 * [changeset:"776/railML"] - Merged changes from branches\stop-activity: New element <stopActivities> added to <stopDescription>, closes #307

### Documentation Tasks
* Document the changes for 2.X
* Create the wiki pages for `stopActivities ` and `stopActivity`