Add option to link Boost dynamically (#1025)

Distributions can guarantee the existence of a specific version of
the Boost libraries, so it makes less sense to link them statically.
Use pkg-config over CMake to find Freetype (#1024)

If pkg-config does not exist on the build system, then the old
FindFreetype.cmake behavior will be fallen back upon, but pkg-config
should be a lot more reliable.
add a note to CMakeLists.txt

(cherry picked from commit a0848af371d451e6ef69918bacf2dd42bf7a6202)
Fix save as scenario for Dialogue.

Add GameCall as fallback mechanism for dialog implementation if no local function is defined.
mac: Zoom in/out main menu commands also work in game mode, call Viewports. methods then
StdScheduler::Added is not necessarily called from the thread the
procedure is meant to be run on, so introduce yet another StdScheduler
extra method StartOnCurrentThread which on Mac OS X does the actual run
loop registration stuff and needs to be called from the actual thread
the scheduler is supposed to run on

StdSchedulerMac: Remove SCHAdditions objects again
cmake: mac: Reorder compiler flag selection a bit
C4NetIO: Place silly poll timeout fix where it actually helps in case of UDP
cmake: mac: Re-add libs bundling, revert to LegacyFindFreeType for APPLE because I don't know