hard equality support

Support for constraints parsing has been implemented. When using:
field => [ '=' => 'condition' ] the condition part won't be SQL:quote'ed
allowing for more flexibility.
fieldlist externalization

Easy access to fieldlist for MarionetteLib classes.
fieldlist & cleanup for MarionetteLib

Potentially more to come at a later commit.
nestedset support

NestedSet trait is still work-in-progress/prototype.

Current support: retrieval, basic add

NestedSet implementation uses simple lft, rgt (not floating point method).