Correct datatype of attribute @sequence
## Description
The attribute `@sequence` of `<associatedNetElement>` has datatype `int`. Since sequences shall start with value 0 and repeatedly increment by 1, the datatype shall be changed to an appropriate type, e.g. `nonNegativeInteger`.
### Background
### Links
## Proposed solution railML 3.2
Change datatype of all attributes `@sequence` to `nonNegativeInteger`.
This affects the following elements:
* `<linearLocation / associatedNetElement>`
* `<netElement / elementCollectionOrdered>`
* _more?_
issue