* added travis.yml for continuous integration
Merge branch 'develop' into task/REN-124

* develop:
  * added travis.yml for continuous integration
correct naming for travis build file
updated dependencies to install for travis
set gcc4.8 as compiler for gcc
Merge pull request #2 from jklimke/task/REN-124

REN-124 Refactored code. Added new option to osgplugin to choose theme
* fixed erroneous handling of files with nonappearance specified
Merge branch 'develop' of https://github.com/3dcl/libcitygml into feature/REN-123-implement-cpack