Version 3.5.0 - Move code around, for the better

Changes

• Integrate line segments, segment_tool is history (#380)
• gaphas.connector is split in gaphas.handle and gaphas.port
• Moved gaphas.aspect module to gaphas package
• Moved gaphas.view.model to gaphas package

This cleanup should reduce the chance of requiring GTK, which is a huge benefit for, for example, the Sphinx extension in Gaphor.