petascope - Default WMS style changed behavior

[Bang Pham Huu]

For v10, WMS default style of a layer needs to change as below:

1. '''if styles are defined''' then the server ''must'' apply one of them
 - if the client specifies style X, then X is applied
 - if the client does not specify a style, then
  - if a default is set on style Y, then Y is applied
  - if no default is set on any style, then Z is applied, where Z is chosen by some consistent criteria, e.g. first style after lexicographic ordering by style name
2. '''if no styles are defined''' then the server returns raw data