Standardise TileElement function names

[duncanspumpkin]

The tile elements surface, track, station, road, signal, building, tree, wall, industry have a number of functions that serve the same purpose. As they access different parts of the struct we can't just have a common function in the TileElementBase but we should at least use the same names for them for each of the elements.

Common functions:

• sequenceIndex (a.k.a. multiTileIndex, sequence, ...). Standardise to sequenceIndex() and setSequenceIndex()
• rotation (a.k.a. unkDirection, direction, ...). Standardise to rotation() and setRotation().

There are some other ones like owner which i think is standardised already. Road and Track share many names should check they are also standardised.