Simplified self.message statements for sheets and projections

Hi,

this is a small PR which changes the message statements.
Previously:
INFO:root:Time: 000000.00 ModelGCAL: Sheets:

INFO:root:Time: 000000.00 ModelGCAL: V1
INFO:root:Time: 000000.00 ModelGCAL: Retina
INFO:root:Time: 000000.00 ModelGCAL: LGNOn
INFO:root:Time: 000000.00 ModelGCAL: LGNOff
INFO:root:Time: 000000.00 ModelGCAL: 


INFO:root:Time: 000000.00 ModelGCAL: Connections:

INFO:root:Time: 000000.00 ModelGCAL: Connect Retina with LGNOn (Match name: afferent_projections, connection name: Afferent)
INFO:root:Time: 000000.00 ModelGCAL: Connect Retina with LGNOff (Match name: afferent_projections, connection name: Afferent)
INFO:root:Time: 000000.00 ModelGCAL: Connect LGNOn with LGNOn (Match name: lateral_gain_control_projections, connection name: LateralGC)
INFO:root:Time: 000000.00 ModelGCAL: Connect LGNOff with LGNOff (Match name: lateral_gain_control_projections, connection name: LateralGC)
INFO:root:Time: 000000.00 ModelGCAL: Connect LGNOn with V1 (Match name: afferent_ON_projections, connection name: LGNOnAfferent)
INFO:root:Time: 000000.00 ModelGCAL: Connect LGNOff with V1 (Match name: afferent_OFF_projections, connection name: LGNOffAfferent)
INFO:root:Time: 000000.00 ModelGCAL: Connect V1 with V1 (Match name: lateral_excitatory_projections, connection name: LateralExcitatory)
INFO:root:Time: 000000.00 ModelGCAL: Connect V1 with V1 (Match name: lateral_inhibitory_projections, connection name: LateralInhibitory)


Now:
INFO:root:Time: 000000.00 ModelGCAL: Level V1: Sheet V1
INFO:root:Time: 000000.00 ModelGCAL: Level Retina: Sheet Retina
INFO:root:Time: 000000.00 ModelGCAL: Level LGN: Sheet LGNOn
INFO:root:Time: 000000.00 ModelGCAL: Level LGN: Sheet LGNOff
INFO:root:Time: 000000.00 ModelGCAL: Match afferent_projections: Connection Retina->LGNOn Afferent
INFO:root:Time: 000000.00 ModelGCAL: Match afferent_projections: Connection Retina->LGNOff Afferent
INFO:root:Time: 000000.00 ModelGCAL: Match lateral_gain_control_projections: Connection LGNOn->LGNOn LateralGC
INFO:root:Time: 000000.00 ModelGCAL: Match lateral_gain_control_projections: Connection LGNOff->LGNOff LateralGC
INFO:root:Time: 000000.00 ModelGCAL: Match afferent_ON_projections: Connection LGNOn->V1 LGNOnAfferent
INFO:root:Time: 000000.00 ModelGCAL: Match afferent_OFF_projections: Connection LGNOff->V1 LGNOffAfferent
INFO:root:Time: 000000.00 ModelGCAL: Match lateral_excitatory_projections: Connection V1->V1 LateralExcitatory
INFO:root:Time: 000000.00 ModelGCAL: Match lateral_inhibitory_projections: Connection V1->V1 LateralInhibitory

Shorter & more precise.