Some updates to AttentionAllocation

1.  Add Scheme functions to get and set the AttentionalFocus Boundary: [cog-get-af-boundary](http://wiki.opencog.org/w/Scheme#cog-get-af-boundary_boundary), [cog-set-af-boundary](http://wiki.opencog.org/w/Scheme#cog-set-af-boundary_boundary)
2. Fix logging in AttentionAllocation modules:
    - Fix the printing of connection matrices and STI vectors for logging
    - Add logs for ImportanceDiffusionAgent, ImportanceSpreadingAgent
3. Add Cython bindings **count_to_confidence** and **confidence_to_count** for the C++ methods **SimpleTruthValue::countToConfidence** and **SimpleTruthValue::confidenceToCount**. Remove the duplicate Python implementation that existed previously.