Training Manual Databases Sections

This PR renames the 2 existing Database Modules. PostgreSQL to "Database Concepts with PostgreSQL" and PostGIS to "Spatial Database Concepts with PostGIS". It updates the content to QGIS 2.0 and for PostGIS 2.x (leaving notes about differences for 1.5). This closes #186 & #187.

The plan is to add an additional module to the workshop on the use of DB Manager and pgAdmin III.