Extract text layout related properties (e.g. displacement, alignments) into seperate object from other placement related text symbolizer properties.
Parse and support placement of multiple text layouts within a single text symbolizer.
Add python binding for Layout node in format tree.
Tests for multiple text layout placements.
Replace tabs with spaces. Remove unused method prototype.
Merge branch 'expr-v2' of github.com:mapnik/mapnik into jmh-text-layouts

Conflicts:
	tests/visual_tests/test.py
Update test cases.
Use make_shared to create shared_ptr.
Update text-multi-layout visual tests to demonstrate placement list with layout nodes and layout/format node nesting. Add new images for line-multi-layout tests.
Merge pull request #2138 from MapQuest/jmh-text-layouts

Multiple text layouts in text symbolizer