[ALOY-737] Integrate xml2tss into style generation

Original PR from @dbankier: [https://github.com/appcelerator/alloy/pull/165](https://github.com/appcelerator/alloy/pull/165)
Ticket: [https://jira.appcelerator.org/browse/ALOY-737](https://jira.appcelerator.org/browse/ALOY-737)

Took functionality from "styles" command and put it into "style" so that `alloy generate style` is the only command. Slightly modified existing unit tests to account for the new style generation format. A few minor code formatting changes.