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