QEP on virtual layers

This QEP covers the addition of "virtual layers" for QGIS, through the use of Spatialite
Ok. This is for geometry columns. Desired types (aka type "affinity") is also available for any columns using PRAGMA table_info('table'). But a null type is also allowed (that's the case if you create a view and SQLite is not able to figure out the type of a column). So this introspection can be used most of the time, but we still need a way for the user to specify columns types.