Binding feature attributes to styles and labels

[sdlime]

This bug will be used to track the implementation of the RFC 19 ​http://mapserver.gis.umn.edu/development/rfc/ms-rfc-19/ implementation.

As of the creation of this bug an initial implementation has been checked in to the main trunk. It supports:

• styles: color, outlinecolor, size and angle
• labels: color, outlinecolor, size and angle

The main remaining tasks are:

• adding a binding for a style symbol
• add more test cases (e.g. what happens when you bind a string to a numeric parameter)
• removal of old properies (e.g. LABELITEMANGLE) and structure members in header files, code, lexer configuration and PHP/MapScript binding
• creation of setBinding and removeBinding MapScript methods for labelObj and styleObj objects (both Swig-based languages and PHP)
• documentation