CMake: include thread lib

- add FIND_PACKAGE(Threads REQUIRED)
- fix cuda_memtest build
- prepare PIConGPU for the same dependencies
Decode allJSON and clean conflict result

- if a merge conflict occures, set the
  failure status and exit in a clean way
- decode all JSON data, not only URLs
  (for example, if someone uses / in a
  branch name)
Merge pull request #35 from ax3l/hotfix/compileSuite-json

Decode all JSON fields and clean conflict result
Merge pull request #34 from ax3l/hotfix/cmake-thread

CMake: include thread lib