Building from scratch fails

[linusdm]

Some hurdles need to be taken when building apex from scratch (a fresh Ubuntu installation):

• Two dependencies missing in compiling_instructions.txt: libfftw3-dev and libssl-dev
• Source files in /apex/src/lib/streamapp/_fromv3 missing. Subfolder core is missing. Fetching it from an older version seems to work.
• Linking fails due to duplicate definitions in /apex/src/lib/apexmain/experimentstore/manageddirectory.cpp and /apex/src/lib/apexmain/experimentstore/manageddirectory.h. Removing them seems to work.

[mh21]

Thanks for the bug report!