Way object duplicates Node data. Ways should only store references to Node ids

#### Broken rules:
`ElementContainer` stores the results of an OSM query as collections of `Node`s, `Way`s and eventually `Relation`s. At present the collection of `Node`s contains values for latitude and longitude of each `Node` and the Key Value pairs scraped from OSM. The `Way` object duplicates these rather than just storing the Node id as a reference.
#### Suggestions to restore compliance:
Switch the `Way` object to store ids only.
While the current system is convenient for converting a `Way` to a polyline (as there is no need to reference the `Node`s) it appears to break the rules and result in unnecessary storage of duplicated data.

'ToUTMPolyline' method will also need updating / refactoring to reference set of Nodes