Implemented:

+ reading of entire ASL file including embedded patterns.
  Supported version is v2 only.
+ writing ASL files without embedded patterns
+ all the ASL parsing happens via intermediate form in XML

Still to be done:

- writing embedded patterns
- connect to actual layer styles

Short description of architecture:

1) KisAslReader reads an ASL file into QDomDocument
2) KisAslXmlParses together with KisAslCallbackObjectCatcher parses
   the prepared XML document and initializes any structures connected
   to it.

3) KisAslXmlWriter is used to create a XML document from internal
   styles representation.
4) KisAslWriter converts XML data prepared by KisAslXmlWriter into
   actual ASL file.