*: massive decruftification & cleanup

- Removed all backends apart from twitter, template, and libpurple.
  (why would you want to use any of them?)
- Deleted dodgy vendored includes (from swiften, boost)
- Replaced all usage of the dodgy SWIFTEN_* macros and HAVE_SWIFTEN_3
  define.
- Removed spectrum2_manager (it's stupid, just use systemd)
- Removed spectrum2 server mode (it's stupid, just use a component)
- Removed Jingle File Transfer (only worked on swiften 3, was suuuper
  hacky)
- Moved spectrum/src to src/ (this always pissed me off)
- Removed WIN32 and non-Linux platform support (was ugly)
- Removed packaging, munin, travis, etc (this is a fork)
- Added .clang-format, ran clang-format everywhere (hooray!)
- Removed half the flags and crap in CMakeLists.txt (it didn't really help)