required libs are not yet grouped

* PluginLib

This reverts merge request !92

Feature qt5.6 support



See merge request !92

As the new glLoad is not compatible with Qt 5.6 we will continue using
glew for now.

This reverts commit 22938119ac1bcf60ad49078c7fa436856bc7c902, reversing
changes made to ed8a9a65a94b8d72b80133d37ddbf4a8c029988a.

Private update



See merge request !85

Only type plugins and the core will access the update function

specification of additional libraries for each plugin to be linked into the core.

also update logo in user documentation sources



See merge request !83

fixes #32 by applying the patch provided by a dielen.

ps: i am still missing around 700 mb mrmory from the provided information, but this is better than before

See merge request !69

New gl loader

on this branch glew was replaced by glLoadgen
Even though the build runs on all platforms, excessive testing should be performed (old opengl cards new ones, runtime tests etc.)
closes #20 

@moebius you probably want to check for code Quality before merging this one.

See merge request !66

Removed FreeFont stuff



See merge request !73