libs: remove boost.log submodule

Upgrade to Boost.Log 2.2, this removes the dependency of this module in
libs/ and makes the manual building obsolete, resulting in a faster
process when building the whole project from scratch.

Note that this lifts the minimum required Boost version to 1.55.0.

Closes #274122
CMakeLists: fix issues with static linkage of Boost libraries

Store HALMD_USE_STATIC_LIBS as cache variable. Otherwise, subsequent
CMake calls would fall back to dynamic linkage.

The Boost.Log library depends on Boost.Filesystem and must be mentioned
first on the command line. The wrong order causes many linker errors:
"undefined reference to `boost::filesystem::something`".