General CMake cleanup/overhaul
* Enable precompiled headers for all projects
* Move specifications itto separate CMakeLists files
* Add openspace-core as a subdirectory
* Move handle_modules functionality into modules/CMakeLists.txt
* Move handleapplications logic into apps/CMakeLists.txt
* Introduce openspace-module-collection interface library to simplify inclusion of modules in applications
* Turn module initialization into a two-step process to adapt to the new minimal dependency scenario
* Compile time speedup
* Remove circular dependencies between modules and core preventing multithreaded compilation on MSVC
* Build Spice multithreaded and as static library
* Remove dependency from core to module-webbrowser
* Remove unused dependency from kameleon
* Remove additional unnecessary dependencies
* Cleanup volume/kameleon/kameleonvolume modules
* Fix visibility issues. Restrict include paths
* Compile kameleon in parallel
* Other cleanup
* Only copy CEF files from one target (hard-coded to OpenSpace right now)
* Remove unused instrumentation code
* Remove the ability to render AABB for globes as it caused a circular dependency between GlobeBrowsing and Debugging
* Removing compiler and cppcheck warnings
* Turn almost all includes into non-system includes
* Don't warn on deprecrated copy
* Updated submodules
* Cleanup
* CMake cleanups
* Update current year
* Update copyright header
* Use script to return list of all modules
* Update credits, license and ghoul
* Add Adam Aslegård's module that renders Gaia mission stars
* Add module for Gaia mission
* Add CCfits and cfitsio submodules and the implemented fitsfilereader module from the OpenSpace-sun-earth-event branch
* Add a TaskRunner to read from a fits file
