[dependencies] migrate to boost 1.54

Currently boost 1.54 already include log library into main line, so
there is no need in custom ppa that was used only because of this
library was only proposal to boost.

Just for remember, ppa URL:
https://launchpad.net/~azat/+archive/boost-unofficial

Also add some TODO's for travis-ci, to migrate into boost 1.54.