start Line and Area builders
use AreaBuilder in XmlThemeBuilder:

- docs
- better Area field naming
update LineBuilder
rename theme style classes
remove LineSymbol
theming changes:

- select="first" also add its renderstyles when no sub-rule matched
  ... before they where only added when one subrule matched

- use select="when-matched" as last subrule in select="first" rules
  instead.
Merge branch 'theme_refactor'
cleanup: move carto theme to not working mapnik tilesource
theme: rename newtron enum
theme: disable (now working) area textures