raised version to 1.5.1-SNAPSHOT
exchanged references to HTTPStatusEvent.HTTP_RESPONSE_STATUS with custom constant (closes #545)

This constant is not always available in pure Flash.
raised version to 1.5.1
updated SWC for 1.5.1
updated changelog for 1.5.1
updated maven pom.xml for v1.5.1
starting development on v1.5.2
added 'color' property to the Button class
optimized TextureAtlas.getNames by caching sorted list of names (closes #548)
Merge branch 'master' into develop