[FEATURE] Compatibility with TYPO3 6.0+

The change adds a new namespaced class that contains basically
the same stuff than the previous class. All occurrences of t3lib_div
have been replaced with the new namespaced class.

In addition the Xclass-Inclusion in ext_localconf.php is modified
and the TYPO3 version dependency in ext_emconf.php is raised to
6.0+

So far it looks as if it's working - needs some deeper testing!
[FEATURE] Implements grunt build and test
[FEATURE] Implements pixel ratios for images
[TASK] Code cleanup and refatcoring
[FEATURE] Adds travis configuration
[RELEASE] 2.0.0-alpha.2
[TASK] Resolves merge conflict
[RELEASE] 2.0.0-alpha.3
[TASK] Updates package instructions
[DOC] Adds travis status image to readme
[TASK] Modifies the test command to include an automatic build
[RELEASE] 2.0.0-alpha.4
[FIX] Failed to load xclass
[FEATURE] Implemets pixel ratios as suggested by mrimann
[TASK] Refactors much of the ImageContentObject xclass
[TASK] Implements cache object

[TODO] Apply pixel ratios to view helper and TYPO3 4.5
[RELEASE] 2.0.0-alpha.5
[FEATURE] Adds pixel ratios to viewhelper
[RELEASE] 2.0.0-alpha.6
[FIX] Resolves #8 by checking for a valid default breakpoint
[TASK] Removes debug option in TS
[TASK] Minor cleanup
[RELEASE] 2.0.0-alpha.7
[TASK] Implemented fluid styling options for viewhelper images
[RELEASE] 2.0.0-beta
[TASK] Consistent naming of style configuration variable