Adding a Pattern to SimpleUnitFormat similar to SimpleQuantityFormat or SimpleDateFormat

[keilw]

Adding a "pattern" similar to SimpleQuantityFormat or SimpleDateFormat to SimpleUnitFormat, so the formatting and parsing could be finer-controlled to use e.g. the name, symbol or label/identifier of a unit.

[keilw]

Moved the priority down, I am not sure, if we really need this beyond methods like getInstance() or getNewInstance().