Removed Travis CI config.
Merge pull request #586 from LaurentGomila/feature/no_travis

Removed Travis CI config.
Fix build of the SFML target on OS X with Xcode
Removed vertical tab support from Text (#442).
Merge pull request #596 from Ceylo/bugfix/595_OSXFrameworkCreation

#595 Fix build of the SFML target on OS X with Xcode

Nevertheless, Xcode generator is not officially supported by SFML
Updated glext, removed glxext.

Removed glxext in favor of the system version.